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
Another Study on Cholesterol, Eggs and CVD Risk
A recent study by Zhong, et al. published in JAMA has been cited in the press including MedicalNewsToday on March 15, 2019. The study analyzed pool data from six prospective studies covering a period up to 31 years (median 17 years follow up) and involving 29,615 men and women in the U.S. It reviewed self-reported intake of cholesterol-containing foods, including eggs, and identified a positive association with an increased risk of cardiovascular disease (CVD) and deaths from other causes.
Here are two analyses of the study:
Note that this was not a systematic review and the findings are not consistent with systematic reviews and meta-analyses of other cohort studies. For more information and practice recommendations, see PEN Practice Question: Are interventions to decrease dietary cholesterol intake (e.g. restricting eggs) recommended for the primary prevention of cardiovascular disease (CVD)?
Further Commentary on the PURE Study: Dairy Intake, Cardiovascular Disease and Mortality
An editorial by Louie and Rangan discusses the findings from the Prospective Urban Rural Epidemiology (PURE) study on the association of total and individual types of dairy food intake with major cardiovascular disease events and mortality (1). The editorial authors report that the PURE study found that higher daily consumption of dairy products may be protective and that the associations were stronger for whole fat dairy foods in low and middle income countries with lower mean dairy intakes (i.e. South and Southeast Asia, Africa and China).
Louie and Rangan point out that while this current analysis is not as affected by the study design issues of other PURE study results, there were large limitations; the most notable being that dietary intakes were only assessed at the beginning of the study (1). A single assessment of dairy consumption may not be an accurate reflection of intakes over the course of the nine years of follow up and this reduces the certainty of the findings. The authors caution that readers should consider this study as only another piece of the evidence, and strong recommendations cannot be made for the consumption of higher fat (versus lower fat) dairy products. The study’s results only suggest that the consumption of dairy products may be encouraged for low and middle income countries and dairy products should not be discouraged for other consumers.
For additional discussion of the PURE study findings, see the PEN Trending Topic: Dairy Intake, Mortality and CVD – The Debate Continues.
- Louie JCY, Rangan AM. No need to change dairy food dietary guidelines yet. Lancet. 2018 Nov 24;392(10161):2242-4. doi: 10.1016/S0140-6736(18)31945-7. Epub 2018 Sep 11. Citation available from: https://www.ncbi.nlm.nih.gov/pubmed/30217461
Misleading News Headline Regarding Egg Consumption
This trial recently appeared in the news, Nutrition Journal Suggests New Guidelines for Egg Consumption, with the researchers concluding that, "a healthy diet based on population guidelines and including more eggs than currently recommended by some countries may be safely consumed". The PEN® System recently updated this Practice Question: Are interventions to decrease cholesterol intake (e.g. restricting eggs) recommended for the secondary prevention of cardiovascular disease (CVD)? The evidence used to answer the question includes a systematic review that reports earlier results of the trial mentioned above along with five other randomized controlled trials, which found that regular egg consumption had no adverse effects on blood lipid levels. All of these trials were assessed at high risk of bias (primarily for lack of allocation concealment and failure to blind participants/personnel) and they all received funding from egg boards/councils. In contrast to these findings, a high egg intake (i.e. >1 egg/day versus <1 egg/week) has been associated with an increased risk of coronary heart disease in individuals with diabetes. A high dietary cholesterol intake (>200 mg/day) can also increase serum cholesterol levels in some people and there is a lack of harm from restricting dietary cholesterol.
Therefore, the PEN recommendation, based on very low quality evidence, suggests restricting dietary cholesterol to ≤200 mg/day (e.g. by reducing egg consumption to <1 egg/week) to reduce CVD events for adults with diabetes, dyslipidemia or established CVD. For practice guidance, see the updated PEN client handout: Eating Guidelines for People with High Blood Cholesterol.
This recommendation does not apply to adults at low CVD risk. For information on eggs for the general population, see PEN Practice Question: Are interventions to decrease dietary cholesterol intake (e.g. restricting eggs) recommended for the primary prevention of cardiovascular disease (CVD)?
Carbohydrate, Fat and Mortality
Reposted January 3, 2018 with an additional dietitian viewpoint*
The study, Associations of Fat and Carbohydrate Intake with Cardiovascular Disease and Mortality in 18 Countries from Five Continents (PURE): A Prospective Cohort Study, stemming from the PURE macronutrient studies, has been getting a lot of press across the globe (e.g. Canada, U.K.). This is a very large international cohort comprising high, middle and low income countries. It is an observational analysis with dietary intake collected by self-reported food frequency questionnaires (FFG) at baseline only. After looking at a range of carbohydrate (46-77% of energy) and saturated fat (2.8-13.2% of energy) intake (not a typical range seen in North America or Europe) the authors found that high carbohydrate intake was associated with a higher risk of total mortality, and non-cardiovascular disease mortality (e.g. cancer, respiratory diseases).
For analysis on the study, see: NHS Choices - Behind the Headlines
For further analysis on the study, see The Conversation: New Study Finding Fat Isn't as Bad as Carbs Misses the Point
*For a dietitian's viewpoint, see: That Viral Study Telling You to Eat More Fat? It's Full of Holes
For more information, see PEN Additional Content:
Practice Question: Is a Reduced Saturated Fat Diet Recommended for Primary or Secondary Cardiovascular Disease Prevention?
Evidence Clip: Butter, Margarine, Saturated and Trans Fats - Making Sense of Research Reported in the News
Benefits of Reducing Saturated Fat Intake Criticized
A recent editorial by Malhotra, et al. made headlines claiming that reducing saturated fat intake has no effect on coronary heart disease. The authors do not cite the best or most recent evidence to support this claim. Importantly, they fail to acknowledge the results of a recent Cochrane review, which found moderate quality evidence that reducing saturated fat intake decreased cardiovascular (CV) events (including CV deaths, CV morbidity or unexplained CV interventions) in populations at low, moderate and high risk (1). When talking about reducing saturated fat intake, it is important to consider the replacement calories. Recent evidence identifies that the greater reductions in CV events occurred when saturated fat was replaced with polyunsaturated fat, but not with carbohydrate (1). The editorial does emphasize the benefits of a whole dietary approach, such as the Mediterranean diet, instead of focusing on specific nutrients. There is merit to this approach. The Mediterranean diet pattern is low in saturated fat and includes rich sources of unsaturated fat such as oils, nuts, seeds and oily fish, in addition to plenty of legumes, vegetables, fruit and whole grains. See additional commentary from David Katz published in Linkedin: Sat-Fat Bait & Switch.
Seems we were not alone in our concerns about the opinion piece that garnered media attention last week. Further expert reaction from the U.K. to the editorial on saturated fat and heart disease is available from Science Media Centre.
See Additional Content: Is a reduced saturated fat diet recommended for primary or secondary cardiovascular disease (CVD) prevention?
Hooper L, Martin N, Adbelhamid A, Dave Smith G. Reduction in saturated fat intake for cardiovascular disease. Cochrane Database Syst Rev. 2015 Jun 10;(6):CD011737. doi.10.1002/14651858.CD011737. Abstract available from: http://www.ncbi.nlm.nih.gov/pubmed/26068959
Article Analysis: Calcium and Heart Health
Cardiovascular Guideline Releases
Article Analysis: Cardiovascular Effects of Exchanging Saturated Fat With an Oil High in Linoleic Acid - Not all Vegetable Oils are Created Equally