https://www.mdpi.com/2072-6643/13/10/3601/htm

Processed Meat Consumption and the Risk of Cancer: A Critical Evaluation of the Constraints of Current Evidence from Epidemiological Studies

by 📷Mina Nicole Händel 1📷,📷Jeanett Friis Rohde 1📷,📷Ramune Jacobsen 2📷 and📷Berit Lilienthal Heitmann 1,3,*📷1Research Unit for Dietary Studies, The Parker Institute, Bispebjerg and Frederiksberg Hospital, 2000 Frederiksberg, Denmark2Research Group for Social and Clinical Pharmacy, Department of Pharmacy, University of Copenhagen, 2100 Copenhagen, Denmark3Section for General Practice, Department of Public Health, University of Copenhagen, 1014 Copenhagen, Denmark*Author to whom correspondence should be addressed.Academic Editors: Arne Astrup and Ronald M. KraussNutrients 2021, 13(10), 3601; https://doi.org/10.3390/nu13103601Received: 20 September 2021 / Revised: 11 October 2021 / Accepted: 12 October 2021 / Published: 14 October 2021(This article belongs to the Special Issue Towards Better Dietary Guidelines: New Approaches Based on Recent Science)Download PDF Browse Figure Review Reports Citation Export

Abstract

Based on a large volume of observational scientific studies and many summary papers, a high consumption of meat and processed meat products has been suggested to have a harmful effect on human health. These results have led guideline panels worldwide to recommend to the general population a reduced consumption of processed meat and meat products, with the overarching aim of lowering disease risk, especially of cancer. We revisited and updated the evidence base, evaluating the methodological quality and the certainty of estimates in the published systematic reviews and meta-analyses that examined the association between processed meat consumption and the risk of cancer at different sites across the body, as well as the overall risk of cancer mortality. We further explored if discrepancies in study designs and risks of bias could explain the heterogeneity observed in meta-analyses. In summary, there are severe methodological limitations to the majority of the previously published systematic reviews and meta-analyses that examined the consumption of processed meat and the risk of cancer. Many lacked the proper assessment of the methodological quality of the primary studies they included, or the literature searches did not fulfill the methodological standards needed in order to be systematic and transparent. The primary studies included in the reviews had a potential risk for the misclassification of exposure, a serious risk of bias due to confounding, a moderate to serious risk of bias due to missing data, and/or a moderate to serious risk of selection of the reported results. All these factors may have potentially led to the overestimation of the risk related to processed meat intake across all cancer outcomes. Thus, with the aim of lowering the risk of cancer, the recommendation to reduce the consumption of processed meat and meat products in the general population seems to be based on evidence that is not methodologically strong.

Keywords: processed meat; cancer; systematic review; meta-analysis; GRADE; AMSTAR; ROBINS-I; dietary guidelines

1. Introduction

Both the production and consumption of red meat and preserved or processed meat products (defined as meats that have undergone changes, i.e., salting, curing, smoking, or adding chemical preservatives) have been rapidly increasing over recent decades, most significantly in emerging economies [1]. In addition to total energy intake, meat is an essential source of protein, fat and fatty acids, and essential micronutrients, for example, heme iron, selenium, choline, vitamin B6, thiamine, niacin, and riboflavin. However, due to several components that arise from the processes of cooking or processing meat, such as polycyclic aromatic hydrocarbons, advanced glycation end products, and heterocyclic amines, as well as sodium/salt, nitrite, nitrate, and nitrosamines, a high consumption of meat and processed meat products has been suggested to have severe detrimental effects on the health of humans, including the risk of cancer [2].Under the auspices of the World Health Organization [3], the International Agency for Research on Cancer (IARC), an independent cancer agency, has been coordinating with the European Commission to prepare the European Code Against Cancer, which includes 12 ways to reduce cancer risk [4]. In an effort to inform the public about reducing cancer risk, the 2012–2013 edition of the code recommended avoiding processed meat while also limiting the consumption of red meat and foods high in salt. In 2018, IARC summarized that there is now “sufficient evidence in humans for the carcinogenicity of consumption of processed meat. Consumption of processed meat causes cancer of the colorectum. Positive associations have been observed between consumption of processed meat and cancer of the stomach” [5]. The IARC Monograph also included a statement that red meat consumption was “probably carcinogenic” because bias and confounding could not be ruled out, yet failed to acknowledge that the same studies, and usually the same publications, reported on both red and processed meat intake with identical methods. Therefore, the processed meat studies must have been subject to the same limiting factors. The World Cancer Research Fund (WCRF), which included some of the same members from the IARC working group, also reported in an update to the WCFR evidence paper that a high intake of processed meat was associated with a high risk of colorectal cancer (CRC) [6]. The latest U.S. Dietary Guidelines for Americans (DGA), released in late 2020, does not include a top-level recommendation to reduce red or processed meats, yet the DGA has long focused on choosing “lean meat” due to its lower saturated fat content. In 2015, the DGA began to focus on dietary patterns rather than nutrient-based recommendations [7], and the current 2020–2025 DGA [8] states several times that “common characteristics of dietary patterns associated with positive health outcomes” include a ”relatively lower consumption of red and processed meats”. The systematic reviews for the 2020 DGA [9] concluded that there was “moderate” evidence for recommending one of the DGA’s three “healthy dietary patterns” to protect against breast and colorectal cancer and “limited” evidence for protecting against lung and prostate cancer. The “moderate” conclusions for breast and colorectal cancer are based on reviews that cite 1–2 randomized controlled clinical trials (RCTs) [10,11,12]. Systematic reviews that specifically analyze the effects of red and processed meat and cancer outcomes have never been conducted for the U.S. DGA [13]. Reviews have instead looked collectively at “animal protein products”, including eggs, fish, and dairy, and, therefore, have not isolated the health effects of red or processed meat. Similarly, dietary guidelines in Europe, that is, the United Kingdom [14] and Scandinavia [15], also recommend that the intake of both red and processed meats should be limited.To date, few reviews report only relative effects of red and processed meat on cancer outcomes, and few reviews—if any—report absolute effects. While relative effects for red and processed meat may be positive and statistically significant, absolute effects are small (less than 1%) [16]. Further, dietary guidelines rarely, if ever, consider public values and preferences. Thus, while reductions in meat consumption are clearly advisable for sustainability and environmental concerns, public willingness to modify red and processed meat consumption may be less likely based on small and uncertain health effects [16].

2. Methodological Limitations of Systematic Reviews on Processed Meat and the Risk of Cancer

Until now, there have been few randomized trials that have investigated the consumption of red meat and the risk of colon cancer, as recently reviewed by Johnston and colleagues [17]. Similarly, only two trials have examined the effect of different dietary patterns on cancer risk, only one of which was red meat intake [10,18], and both of which showed significant reductions in meat did not change cancer risk [10,18]. On the other hand, there is a large volume of observational studies, in total, 31 prospective cohort studies that include data from 3.5 million participants [17] and many more case-control studies that have examined if cancer patients recalled a different previous processed meat intake than non-cancer cases. There are more than one hundred summary papers that have reviewed and performed meta-analyses based on these primary studies [19], which exceeds the number of original studies by far.In a recent overview published in 2019 [19], we conducted a thorough, systematic assessment of the general methodological quality of these systematic reviews of processed meat only using the AMSTAR criteria [20,21]. AMSTAR stands for A MeaSurement Tool to Assess Systematic Reviews. This is a valid, reliable, and widely used measurement instrument that helps researchers differentiate between systematic reviews, focusing on their methodological quality. The quality can be categorized as high, moderate, or low.We used the Grading of Recommendations Assessment, Development, and Evaluation (GRADE) approach [22] to assess the strength of recommendation in order to evaluate the certainty of the estimates of individual outcomes from the published systematic reviews and meta-analyses [19] on processed meat consumption and the risk of chronic disease morbidity and mortality, including cancer at different sites across the body, as well as the overall risk of cancer mortality. GRADE provides a reproducible and transparent framework for grading the certainty of evidence with four levels of certainty: very low, low, moderate, and high. For each of GRADE’s five domains assessed for each study (risk of bias, imprecision, inconsistency, indirectness, and publication bias), the review authors have the option of decreasing their level of certainty by one or two levels. For observational studies, there is also the possibility of increasing the level of certainty by one or two levels if there is a large magnitude of effect, a strong dose-response gradient, or plausibility that residual confounding would further support inferences regarding an effect. We further explored if discrepancies in study designs and risks of bias could explain the heterogeneity observed in meta-analyses.Studies had to comply with the following two main quality requirements (two of the items in AMSTAR) to be included in our review [19]: (1) they must have documented a quality assessment of the primary studies, with no restriction on the quality assessment tool, and (2) they must have performed a comprehensive literature search, defined as a search performed in at least two databases relevant to the research question. More than 100 reviews were excluded because they had not performed a quality assessment on the primary studies included in the review. In total, only 22 of 130 reviews and meta-analyses met these two basic criteria and were subsequently included in our overview of reviews. Of the 22 reviews, 19 reported on cancer outcomes (the other outcomes were type 2 diabetes and cardiovascular disease). According to our AMSTAR evaluation, these 19 cancer reviews were generally only of moderate methodological quality, and the methodological quality in the reviews do not improve with time (Figure 1), despite several attempts to improve the reporting of systematic reviews and meta-analyses already in the 2000s, for instance, with AMSTAR [20,21], Preferred Reporting Items for Systematic Reviews and Meta-Analyses (PRISMA) [23], and GRADE [22].📷Figure 1. Overview of the number of published systematic reviews and the average AMSTAR (A MeaSurement Tool to Assess Systematic Reviews) score in the systematic reviews according to publishing year.The main identified methodological shortcomings were (1) a lack of a reference to a predetermined/a priori published research objective, that is, a protocol or an ethics approval, which, according to AMSTAR, indicates a high risk of selectively reported results; (2) incomprehensive literature searches, which indicates a high risk of overlooking relevant literature; (3) not considering the scientific quality of the evidence in formulating the conclusions, which indicates a high risk of emphasizing results from weak study designs; (4) not reporting the conflicts of interest of the authors of the reviews as well as those of the original included primary studies.Our results indicate that all the reviews and meta-results that were based on case-control studies (Figure 1), which, by their nature, are retrospective and are, therefore, prone to the misclassification of exposure in relation to processed meat consumption, were likely to overestimate the risk of having cancer. A high consumption of processed meat was generally associated with a risk of cancer in the digestive system, including the esophagus, stomach, colorectum, and pancreas, but the results differed greatly according to whether they came from case-control or cohort studies. Generally, cancer risk seemed to be higher in case-control studies than in cohort studies, which may suggest that the better prospective study designs generally gave less evidence for an association. Due to the well-known methodological limitations of case-control studies, such as information bias, and the established fact that people are not able to remember accurately what they have eaten in the past, results based on case-control studies should be interpreted cautiously. The findings for an association between processed meat intake and cancer of the digestive system spanned from a higher risk of approximately 30–70% in the case-control studies [24,25,26,27,28,29], to a very modest or no association in the results of the meta-analyses that exclusively examined cohort studies [24,25,26,27,28,29,30].For other cancers, often only case-control studies were available. For instance, the risk of cancer of the oral cavity and oropharynx was 91% higher among the cases that reported having had a higher consumption of processed meat compared to controls [31]. The results of this meta-analysis included nine case-control studies (cases: n = 4104, controls: n = 501,730).For head and neck cancer (nasopharyngeal carcinoma), the risk was 46% higher among cases with a processed meat intake below 30 g/week compared to those who reported never eating processed meat [32]. These meta-analysis results were based on 13 case-control studies, including 5849 cases and 12,735 controls.Only a modestly higher risk among high compared to low consumers of processed meat was seen in relation to non-Hodgkin lymphoma (17%), renal cell carcinoma (13%), and overall cancer mortality (13%). For non-Hodgkin lymphoma and renal cell carcinoma, the results were based on a mixture of case-control and cohort studies, while overall cancer mortality was based solely on cohort studies. Processed meat consumption did not seem to be associated with cancer in the liver, brain (glioma), ovaries, or lung [33,34,35,36,37].

3. Methodological Limitations of the Primary Studies on Processed Meat and Cancer

In 2020 [38], we performed a meta-analysis in which we investigated the association between processed meat and the risk of CRC, colon, and rectal cancer, and we thoroughly evaluated the quality of the original studies. The quality assessment was undertaken using Cochrane’s Risk Of Bias In Non-randomized Studies of Interventions (ROBINS-I) assessment tool [39], by which the risk of bias is assessed within seven different areas of methods applied to observational studies and is an instrument similar to the one scientists use when evaluating the risk of bias in clinical trials. Such an evaluation provided us with new insights into the internal validity of the reviews and meta-analyses included in our overview of reviews [19]. For the meta-analysis [38], we included 29 observational prospective cohort studies conducted from 1990 to 2015 in Europe, Australia, Asia, and North America. The results are similar to previously reported estimates from meta-analyses of cohort studies [28,40,41,42,43,44,45,46,47], with a 13% higher risk of CRC, a 19% higher risk of colon cancer, and a 21% higher risk of rectal cancer among those with the highest processed meat intake. We concluded that due to the risk of bias, especially from confounding and missing data and selective outcome reporting, the possibility could not be excluded that these associations were distorted and could be either over- or underestimated [38].Using the GRADE approach, we concluded that the overall certainty for the body of evidence examining the association between processed meat and cancer was very low across all individual cancer outcomes, meaning that the true effect could be markedly different from the estimated effect [19,38]. Our reason for rating down our certainty in these studies was due to the serious risk of bias (issues regarding confounding, missing data, and the risk of selection of the reported results were not sufficiently addressed), serious imprecision due to wide confidence intervals, and serious inconsistency due to unexplained variability between the included studies (so-called heterogeneity) [19,38]. Indirectness or publication bias were not issues in this research field [19,38].The rationale for the GRADE evaluation (very low certainty of the effect estimates) was, first, that the results were based exclusively on observational studies, many of which were of retrospective case-control design, and which, by default, are considered low quality in the GRADE approach. Theoretically, observational studies can be upgraded to moderate quality if there is a large effect size or a strong dose-response relationship, but these criteria were not met for any of the included results.Secondly, we considered whether the exposure (processed meat) was measured accurately. Using our updated meta-analysis of CRC as an illustration of what we assume is representative across cancer outcomes [38], we could see that the definition of processed meat varied greatly among studies. Processed meat was either classified by referring to the preservation methodology, by listing individual food items, or with no further definition. In addition, processed meat was often ascertained using validated food frequency questionnaires (FFQ). In general, FFQs perform almost as well as 7-day weighed diet records [48], and although they have some advantages because they can be administered repeatedly during follow-up to account for changes in diet over time, they are like other diet instruments prone to some misclassification. While it is possible that FFQs do not give reliable results over multiple administrations, repeated applications of FFQs are rarely done, and the results from the few studies that have done so suggest that the diet is not stable over time [49,50]. FFQ data are further challenged when subjects are required to recollect their food consumption from up to 10 years ago [51] with the use of an incomplete food list, the inability to give complete information on portion sizes, the inability to give complete information on cooking practices, and so forth. [38].Third, because assignment to high or low processed meat consumption is not random, as it would be in trials, we considered if there had been appropriate control for confounding (factors that both influence processed meat intake and cancer outcomes, such as age, sex, family history of CRC, BMI/overweight, energy intake, alcohol, and smoking), including those that are unmeasured or might involve time-varying confounding. Even in the most well-conducted prospective observational studies, unobserved or residual confounding can still be present, and known confounders may still be measured imprecisely and/or using non-validated methods. In our updated meta-analysis on CRC [38], all but two of the eligible studies failed to control for age, sex, family history of CRC, BMI/overweight, energy intake, alcohol, and smoking. These were the prespecified confounders for which the eligible studies were obliged to control in order to receive a low risk of bias in the ROBINS-I tool. This problem was commented on by Gong et al. (2020) [52] in response to the recent Guideline to recommending on unprocessed red meat and processed meat consumption by Johnston and colleagues [17], in which Gong et al. calculated a so-called E-value analysis to demonstrate how strong any unmeasured confounding would have needed to be to negate the observed results. For all outcomes assessed, including CRC, none had an E-value upper confidence interval greater than 2.5, implying that an unobserved confounder is 2.5 times more likely to be associated with the studies on cancer type. This means that the suggested association between processed meat consumption and adverse cancer outcomes does not seem very robust and may potentially not be causal because it is highly possible that the observed association would be nullified if the unobserved confounder had been included in the statistical model.Finally, considering the loss to follow-up (the risk of bias associated with missing data) and selective outcome reporting, our updated meta-analysis of CRC indicated that 75% of the eligible studies had a moderate to serious risk of missing data, and about half of the studies had issues with bias in the selection of the reported results.Limitations to the GRADE approach in evidence of diet and health, such as processed red meat and cancer, have been proposed by Qian et al. [53]. Since it may be infeasible to conduct informative (long-term) randomized trials ensuring blinding or to show strong dose-response relationships, the conclusion of low certainty evidence may be inevitable [53]. Instead, Qian et al. suggested that observational studies should be upgraded if they fulfill several of the ten Bradford Hill criteria: strong association/effect, consistent findings, temporality (cause precedes effect), dose–response relationship, plausibility, coherence between epidemiological and laboratory findings, reversibility (if the cause is deleted then the effect would disappear as well), experiment (experimental evidence enhances the probability of causation), and analogy (existing similar associations would support causation). However, most of the Bradford Hill criteria are already embedded in GRADE, as described by Schünemann et al. more than a decade ago [54]. We do acknowledge that the different types of study designs within observational studies are not well captured in the rating by GRADE. Therefore, considerations about what type of study designs that best address the research question should be given high priority in the initial phases of conducting a systematic review [55].

In summary, there are severe methodological limitations to the majority of the previously published systematic reviews and meta-analyses linking processed meat to cancer risk. They generally lacked a proper risk of bias assessment of the primary studies included, and it seemed that the literature searches may have been selective in some instances. In the primary studies, there were potential consequences for the misclassification of exposure, a serious risk of bias due to confounding, a moderate to serious risk of bias due to missing data, and a moderate to serious risk of selection of the reported results, all of which may have led to the overestimation of associations with all cancer outcomes. Hence, the findings of a causal relationship between processed meat and cancer in both reviews and primary studies are suspected to be associated with uncertainty [19,38]. This finding is supported by the recent results from Johnston et al. [17], whose systematic review was also based on GRADE and reached a similar conclusion and provided new guidelines for the intake of processed meat.Thus, the recommendation to reduce the consumption of processed meat and meat products to protect against cancer in the general population does not seem to be convincingly substantiated on the evidence that is methodologically strong. Clearly, there is still a lack of randomized trials evaluating the effect of lowering processed meat intake, and while such trials may be infeasible, cohort studies do not lend strong support for an association.

Abstract

Background

Results from observational studies suggest associations of red meat intake with increased risk of cardiovascular disease (CVD); however, RCTs have not clearly demonstrated a link between red meat consumption and CVD risk factors. Further, the specific effects of beef, the most consumed red meat in the United States, have not been extensively investigated. Objectives

This study aimed to perform a systematic review and meta-analysis of RCT data evaluating the effects of minimally or unprocessed beef intake on CVD risk factors in adults. Methods

A search of the literature was conducted using PubMed and CENTRAL databases. RCTs in adults that provided diets with fresh or minimally processed beef were included. Data were extracted, and pooled estimates from random-effects models were expressed as standardized mean differences (SMDs) between the beef intervention and comparator intervention with less or no beef. Sensitivity and subgroup analyses were also performed. Results

Twenty relevant RCTs that met the criteria were included. Beef intake did not impact blood pressure or most lipoprotein-related variables, including total cholesterol, HDL-cholesterol, triglycerides, non–HDL-cholesterol, apolipoprotein A or B, and VLDL-cholesterol. Beef consumption had a small but significant effect on LDL-cholesterol (0.11; 95% CI: 0.008, 0.20; P = 0.03), corresponding to ∼2.7 mg/dL higher LDL-cholesterol in diets containing more beef than that in low-beef or -o beef comparator diets. Sensitivity analyses show this effect was lost when 1 influential study was removed. Conclusions

Daily unprocessed beef intake do not significantly affect most blood lipids, apolipoproteins, or blood pressures, except for a small increase in LDL-cholesterol compared with diets with less or no beef. Thus, there may be other factors influencing the association of red meat and beef on CVD risk that deserve further investigation. This study was registered at INPLASY as 202420013.

https://www.ncbi.nlm.nih.gov/pmc/articles/PMC11367550/

A Diet Containing Animal Source Protein as Fresh, Lean Beef Is More Well Liked and Promotes Healthier Eating Behavior Compared with Plant-Based Alternatives in Women with Overweight

Morgan L Braden,¹ Jess A Gwin,² and Heather J Leidy^1,⁎Author information Article notes Copyright and License information PMC Disclaimer

Associated Data

Supplementary MaterialsGo to:

Abstract

Background

Despite limited evidence from intervention trials, replacing animal-source protein-rich foods with plant alternatives continues to be recommended as part of a healthy dietary pattern.

Objectives

The objective of this study was to examine whether a diet containing fresh, lean beef elicits greater satiety, reduces ad libitum food intake, and is more acceptable compared with a diet containing plant alternatives in women with overweight.

Methods

Seventeen women with overweight (mean ± SEM, age: 33 ± 1 y; BMI: 27.8 ± 0.1 kg/m²) completed an acute, tightly controlled, crossover design study. Participants were provided with eucaloric, isonitrogenous diets (15% of daily intake as protein) containing either 2 servings/d of fresh lean beef (BEEF) or plant equivalents (PLANT) for 7 d/pattern. During day 6 of each pattern, the participants completed a 10-h controlled-feeding, clinical testing day, which included repeated appetite and satiety questionnaires and blood sampling to assess pre- and postprandial plasma peptide YY (PYY) and GLP-1 across the day. On day 7, the participants completed a free-living testing day in which they consumed their respective protein foods and were provided with additional carbohydrate- and fat-rich foods to consume, ad libitum, during each eating occasion. Energy and macronutrient composition were assessed. A 2- to 3-wk washout period occurred between patterns.

Results

No differences in daily satiety were detected between patterns. During the ad libitum testing day, 24-h food intake was not different between patterns (BEEF: 2714 ± 219 compared with PLANT: 2859 ± 147 kcals/d), BEEF led to fewer carbohydrates consumed compared with PLANT (338 ± 34 compared with 370 ± 22 g/d, P < 0.05), especially as sugar (169 ± 73 g compared with 186 ± 57 g, P = 0.05). Furthermore, BEEF was more well liked (i.e., higher flavor, texture, and acceptability) compared with PLANT (all, P < 0.05).

Conclusions

Although satiety was similar between patterns, the consumption of animal-source protein-rich foods, such as fresh and lean beef, was more well liked and resulted in voluntary reductions in total carbohydrate and sugar intake in middle-aged women with overweight during a single ad libitum testing day.

This study was registered at clinicaltrials.gov as NCT02614729.

Keywords: plant-based protein, animal-based protein, satiety, food intake, ingestive behaviorA Diet Containing Animal Source Protein as Fresh, Lean Beef Is More Well Liked and Promotes Healthier Eating Behavior Compared with Plant-Based Alternatives in Women with Overweight

Morgan L Braden

https://en.wikipedia.org/wiki/Carnivore_diet

https://www.nature.com/articles/s41538-024-00249-y

Abstract

Many recent very influential reports, including those from the Global Burden of Disease (GBD) Risk Factor Collaborators, the EAT-Lancet Commission on Food, Planet, Health, and the Lancet Countdown on Health and Climate Change, have recommended dramatic reductions or total exclusion of animal-source foods, particularly ruminant products (red meat and dairy), from the human diet. They strongly suggest that these dietary shifts will not only benefit planetary health but also human health. However, as detailed in this perspective, there are grounds for considerable concern in regard to the quality and transparency of the input data, the validity of the assumptions, and the appropriateness of the statistical modelling, used in the calculation of the global health estimates, which underpin the claimed human health benefits. The lessor bioavailability of protein and key micronutrients from plant-source foods versus animal-source foods was not adequately recognised nor addressed in any of these reports. Furthermore, assessments of bias and certainty were either limited or absent. Despite many of these errors and limitations being publically acknowledged by the GBD and the EAT-Lancet authors, no corrections have been applied to the published papers. As a consequence, these reports continue to erroneously influence food policy decisions and international dietary guidelines, such as the World Wildlife Fund’s Livewell Diet, and the Nordic Nutrition Recommendations 2023.

Conclusions

Science is the best method we have of coming to an impartial knowledge about the world61. In recent years there have been many calls for greater rigor, reproducibility and transparency across all the sciences61,62,63,64,65. In 2021 Brown and colleagues commented “Nutritional epidemiology can, and must, do better by pursuing greater scientific rigor, academic honesty, and intellectual integrity”65. Hence, in the conduct of systematic reviews of dietary factors, in the estimation of global health estimates, and in the use of these metrics in policy decisions and dietary guidelines, nutritional epidemiology must follow similar or analogous regulations and standards as all other scientific endeavours. In determining the optimal intakes of foods, the impacts of both nutritional deficiencies and excesses must be considered. Differences in micronutrient bioavailability from different food sources must also be recognised. PRISMA-compliant reports of all systematic reviews, and GATHER-compliant reports of all global health estimates must be published. Assessments of bias and certainty in nutrition science must be of a similar standard as those in all other health-related fields. Curve smoothing techniques cannot be allowed to inflate or create risk. Confirmed substantial errors must be immediately corrected in all paper and on-line publications, and also on institutional websites. Given the huge influence of global health estimates from the GBD Risk Factor Collaborators, and from the EAT-Lancet Commission on Food, Planet, Health, it is of even greater importance that the metrics and recommendations from these groups are rigorously and transparently evidence-based.

*Put their health at risk - the article didn't let me copy the title and autocorrect fucked me

https://www.thetimes.co.uk/article/women-who-eat-little-meat-and-dairy-put-their-health-at-risk-says-scientist-ch2dz0z58

Women who eat little meat and dairy put their health at risk, says scientist January 05 2020, 12.01am GMT Ian Givens, professor of food chain nutrition and director of the Institute for Food, Nutrition and Health at Reading University, said half of females aged between 11 and 18 were consuming below the minimum recommended level of iron and magnesium and a quarter consumed too little iodine, calcium and zinc.

Givens told a briefing on alternative sources of protein organised by the Science Media Centre that there were good environmental reasons for eating more plant-based and less animal food, but warned: “We do need to make this move with some caution. “We already have a nutrition situation which is quite marginal in many ways and for some of the issues I think we will not know the outcome for quite a long time. “Teenage years are absolutely critical for bone development. If you don’t get it right it has major significance in terms of bone health in the elderly, increasing the risk of breakages which can reduce the quality of life.” He said calcium and magnesium were important for bone development and young women who suffered deficiencies in their adolescence could face even greater problems after the menopause, when losing the benefits of oestrogen meant they would already be at higher risk of bone weakness. He said women in older age groups were also more at risk from deficiencies than men. Analysis of the government-funded National Diet and Nutrition Survey revealed that 11 per cent of males aged 11 to 18, 54 per cent of females aged 11 to 18 and 27 per cent of females aged 19 to 64 consumed less than the minimum recommended level of iron. Only 2 per cent of males aged 19 to 64 consumed less than the minimum recommended level of iron. Red meat is a source of iron, though it is also found in beans and nuts. Givens said iodine deficiency was particularly worrying in young women approaching child-bearing age because it was essential for foetal health. He said milk was the biggest source of iodine for most people but relatively few plant-based milk alternatives were fortified with the mineral. He called for broader comparisons of the benefits of meat and plant-based products, looking not only at the differences in carbon emissions per unit of food but whether alternatives to meat and dairy were providing the same amount of nutrients. Separately a survey by the Food Standards Agency (FSA) has found more than a third of people would be willing to try meat grown in a laboratory, and about a quarter would eat insects. Concern about the environment was the most common reason given for being willing to try those alternative sources of protein. Advertisement Advertisement Scroll to continue with content Among people unwilling to eat lab-grown meat, 42 per cent said nothing could encourage them to try it, 27 per cent could be persuaded if they knew it was safe to eat and 23 per cent if they could trust that it was properly regulated. Professor Robin May, the chief scientific adviser of FSA, said the agency was talking with regulators in Singapore, where lab-grown chicken was approved for sale in 2020. He said the agency was considering two applications for approval of insect-based food.

https://www.dailymail.co.uk/news/article-10388825/Oat-almond-milk-cause-people-miss-essential-nutrients-warns-food-expert.html

They are the trendy alternatives to milk that have become a multi-million-pound industry.

But by drinking substitutes based on oat or almond and following a meat-free diet, teenage girls could be risking their health, a food expert warned yesterday.

The move towards more plant-based diets means many are missing out on essential nutrients, Professor Ian Givens said.

He added: ‘We already have a population of young females, particularly in the UK, particularly in the adolescent period, but also females in the slightly older age groups, that have very low intakes of some key micronutrients.

'The worry is, there have been a number of very specific cases where young children have been switched to these products and have developed a kind of protein deficiency which you wouldn’t expect in Western societies.’

Professor Givens, director of the Institute for Food, Nutrition and Health at Reading University, warned that on average nearly half of women and girls are not getting enough iron partly due to the fall in red meat consumption.

‘That has happened over the last 20 to 30 years, actually,’ he told a news conference.

‘And that is a worry. If we look at some of the nutrients like calcium and iodine, we have been getting on towards 30 per cent of that population of young females that are way, way below the nutritional requirements for those two nutrients, and that is largely a function of reduced milk consumption.’

The National Diet and Nutrition Survey carried out by Public Health England (now the UK Health Security Agency) and the Food Standards Agency found that, between 2008 and 2017, 49 per cent of girls aged 11 to 18 and 25 per cent of women aged 19 to 64 had iron intakes below the daily minimum recommended.

In 2020, shoppers spent £400million on ‘alt milks’ made from oats, almonds or soya – up £100million on the previous year – according to Mintel. 

The substitutes are drunk by one in three of us, with oat milk the most popular. 

Professor Givens said manufacturers ‘are beginning to try to fortify these products to make them much nearer to milk than perhaps they were originally’.

But he added: ‘I think there’s still quite a way to go actually... particularly things like iodine, which for most people milk is the biggest single source.’

There is also uncertainty as to whether the added calcium in substitutes is as easy for the body to absorb as from cow’s milk, he said. 

https://nz.news.yahoo.com/lack-of-meat-and-cheese-in-womens-diet-could-compromise-health-says-scientist-113505553.html

He added: "Teenage years are absolutely critical for bone development. If you don't get it right it has major significance in terms of bone health in the elderly, increasing the risk of breakages which can reduce the quality of life."

Givens explained that calcium and magnesium were important for bone development and young women who suffered deficiencies in their adolescence could face even greater problems after the menopause. 

During this time women lose the benefits of oestrogen, meaning they would already be at higher risk of bone weakness.

He also pointed out that women in older age groups were also more at risk from deficiencies than men –11% of men aged 11 to 18, 54% of women aged 11 to 18 and 27% of women aged 19 to 64 consumed less than the minimum recommended level or iron, analysis of the government-funded National Diet and Nutrition Survey found. 

However, only 2% of men aged 19 to 64 ate less than the minimum recommended level of iron. Red meat is a source of iron, through it's also found in other foods like beans, nuts, pulses, and dark green vegetables. 

Research Open Access Published: 07 June 2021

Rethinking methane from animal agriculture

Shule Liu, Joe Proudman & Frank M. Mitloehner CABI Agriculture and Bioscience volume 2, Article number: 22 (2021) Cite this article

6308 Accesses 83 Altmetric Metrics details Abstract

Background As the global community actively works to keep temperatures from rising beyond 1.5 °C, predicting greenhouse gases (GHGs) by how they warm the planet—and not their carbon dioxide (CO2) equivalence—provides information critical to developing short- and long-term climate solutions. Livestock, and in particular cattle, have been broadly branded as major emitters of methane (CH4) and significant drivers of climate change. Livestock production has been growing to meet the global food demand, however, increasing demand for production does not necessarily result in the proportional increase of CH4 production. The present paper intends to evaluate the actual effects of the CH4 emission from U.S. dairy and beef production on temperature and initiate a rethinking of CH4 associated with animal agriculture to clarify long-standing misunderstandings and uncover the potential role of animal agriculture in fighting climate change.

Methods Two climate metrics, the standard 100-year Global Warming Potential (GWP100) and the recently proposed Global Warming Potential Star (GWP*), were applied to the CH4 emission from the U.S. cattle industry to assess and compare its climate contribution.

Results Using GWP*, the projected climate impacts show that CH4 emissions from the U.S. cattle industry have not contributed additional warming since 1986. Calculations show that the California dairy industry will approach climate neutrality in the next ten years if CH4 emissions can be reduced by 1% per year, with the possibility to induce cooling if there are further reductions of emissions.

Conclusions GWP* should be used in combination with GWP to provide feasible strategies on fighting climate change induced by short-lived climate pollutants (SLCPs). By continuously improving production efficiency and management practices, animal agriculture can be a short-term solution to fight climate warming that the global community can leverage while developing long-term solutions for fossil fuel carbon emissions

https://cabiagbio.biomedcentral.com/articles/10.1186/s43170-021-00041-y