Trending Topics pieces (Article Analyses, Evidence Clips and Other Topics) are published in timely response to recent media and journal articles, position statements, clinical guidelines, etc. Since they are based on the most recent evidence/publications, they may not be consistent with PEN evidence in other PEN content areas. As soon as possible, when this occurs, the PEN content will be reviewed and updated as needed.
Animal and Plant-based Protein Foods Effects on Blood Lipid Levels
A recent randomized control trial of atherogenic lipid levels was reported in the American Journal of Clinical Nutrition (1). Participants were randomly assigned to either high (∼14% total energy) or low (∼7% total energy) saturated fat (SFA). Within each of these arms participants were further randomized to various sources of protein (red meat, white poultry meat, plant-based protein (legumes, nuts, grains, isoflavone-free soy products)) and tested in a factorial crossover design. This design was used to test both the effects of different levels of saturated fat and the various protein sources. The leanest cuts of red and white meat were used with all visible fat and poultry skin removed. All food (standardized entrées, side dishes, caloric beverages, snacks) was provided (except for fruit and vegetables, to ensure freshness) to the participants. Diet energy was individualized to ensure weight maintenance. The higher SFA was mostly from butter and full-fat dairy products, replaced with monounsaturated fats in the lower SFA arms. Participants, aged 21-65 years, were of good health; 113 of the 177 enrolled (63%) completed the study. Diets were consumed for four weeks with a two to seven-week washout period in between. Primary outcomes were LDL cholesterol, apoB, small plus medium LDL and the total/HDL cholesterol ratio.
Results and Conclusions
The trial revealed that, independent of SFA content, low density lipoprotein (LDL) cholesterol and apoB were higher with white and red meat than with plant-based protein (P<0.0005 for all) (1). Total/high density lipoprotein and small plus medium LDL cholesterol were not affected by protein source (P=0.51 and P=0.10). There were no significant differences between red and white meat on other primary outcomes. Furthermore, high SFA intakes increased LDL cholesterol (P=0.0004, apoB (P=0.0002) and large LDL (P=0.0002) compared with low SFA, independent of protein source.
The authors concluded that their findings support current guidelines of promoting increased consumption of plant-based foods for reducing CVD risk (1). The study was not able to conclude that choosing lean white meat offered advantages over lean red meat for reducing CVD risk.
PEN Evidence Analyst Analysis
The strengths of this study include:
- It was a randomized trial (with concealed allocation using numbered envelopes so the researchers would not be aware of the next randomization sequence.
- It was a cross-over design (participants were their own controls).
- Participants were provided with the food.
This study avoided confounding by three of the elements of the design. First by randomization to the order of the diets, second by using the participants as their own controls, and third by providing most of the food to the participants, to avoid confounding by other dietary factors.
A limitation of this study is that it does not refer to higher fat meats since blood lipid effects were only examined after the consumption of only very lean meats. A second limitation is the indirectness of the blood levels, which may not directly predict cardiovascular disease.
For additional interpretation of the study, see: https://theconversation.com/research-check-is-white-meat-as-bad-for-your-cholesterol-levels-as-red-meat-118390.
- Bergeron N, Chiu S, Williams PT, M King S, Krauss RM. Effects of red meat, white meat, and nonmeat protein sources on atherogenic lipoprotein measures in the context of low compared with high saturated fat intake: a randomized controlled trial. Am J Clin Nutr. 2019 Jun 4. pii: nqz035. doi: 10.1093/ajcn/nqz035. [Epub ahead of print]. Abstract available from: https://www.ncbi.nlm.nih.gov/pubmed/31161217
Red Meat, Comparison Diets and CVD
A new meta-analysis of random control studies looked at the effects of red meat consumption and risk factors for cardiovascular disease (blood lipids, apolipoproteins, blood pressure) (1). The meta-analysis involved 1,803 participants from 36 RCTs that compared red meat diets with diets that replaced red meat with a variety of foods. The study found that the results depended on the composition of the comparison diet: there were improvements in blood lipids when red meat was substituted with high quality plant protein sources but not when replaced with low quality carbohydrates. The senior author of the study, Meir Stampfer, stated: “Asking 'Is red meat good or bad?' is useless,"…. "It has to be 'Compared to what?' If you replace burgers with cookies or fries, you don't get healthier. But if you replace red meat with healthy plant protein sources, like nuts and beans, you get a health benefit" (1).
PEN Team Comment:
This study combined the results from 36 randomized controlled trials. Randomized controlled trials can give more certainty of the findings. If the trials were well-designed and conducted, the intervention and control groups should be similar, providing confidence that any differences in outcome were due to the intervention compared to the comparison group. The confidence intervals from the individual studies (seen as the horizontal lines for each study in the Figures) were wide, indicating variability in the results and/or small sample sizes.
In addition, this study identified one of the difficulties of nutrition trials: “Inconsistencies regarding the effects of red meat on cardiovascular disease risk factors are attributable, in part, to the composition of the comparison diet” (2).
- ScienceDaily. Substituting healthy plant proteins for red meat lowers risk for heart disease. 2019 Apr 9. Available from: https://www.sciencedaily.com/releases/2019/04/190409141808.htm
- Guasch-Ferre M, Satija A, Blondin SA, Janiszewski M, Emlen E, O’Connor LE, et al. Meta-analysis of randomized controlled trials of red meat consumption in comparison with various comparison diets or cardiovascular risk factors. Circulation. 2019 Apr 9;139(15):1828-45. doi:10.1161/CIRCULATIONAHA.118.035225. Abstract available from: https://www.ncbi.nlm.nih.gov/pubmed/30958719
WHO Report on Meat and Cancer
While WHO's International Agency for Research on Cancer (AICR) report reclassifies carcinogenic groups, the recommendation remains the same - avoid processed meats and eating no more than 18 ounces (~500 gm) of cooked red meat weekly to lower colorectal cancer risk. Cancer Research UK explain how the cancer classification system works and what the risks are. Marion Nestle provides some comments on the meat-is-carcinogenic report. Also see past Article Analysis: Red Meat Consumption and Mortality. Further message from WHO October 29, 2015: