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