New study questions one-size-fits-all dietary guidelines for heart health

By Dr. Liji Thomas, MDReviewed by Benedette Cuffari, M.Sc.Aug 30 2023

A new study published in the journal Global Epidemiology discusses some of the limitations associated with healthy dietary recommendations for the general public.

Study: Associations of animal source foods, cardiovascular disease history, and health behaviors from the national health and nutrition examination survey: 2013–2016. Image Credit: eggeegg / Shutterstock.com

Introduction

Epidemiology uses data from observations made at the population level, thus capturing the effects of interventions in real-world settings. Compared to randomized controlled trials (RCTs), wherein patient populations and therapeutic interventions are highly controlled, epidemiological studies are at a greater risk of bias due to the inability to ensure that study populations are comparable.

Many studies indicate a reduced risk of cardiovascular disease (CVD) with a lower intake of animal-source foods (ASFs) and greater consumption of plant-based foods. In addition, fiber-containing foods contributing 40-55% of the total energy intake are linked to a longer lifespan and lower coronary heart disease (CHD) risk and diabetes risk.

Consuming red and processed meat is associated with a greater risk of colon, lung, esophagus, and stomach cancers. Comparatively, white meat is associated with a reduced risk of CVDs and cancer.

Obese and diabetic subjects have experienced significant improvements in CVD and diabetes, respectively, after consuming diets low in carbohydrates. This is despite the higher amount of ASFs incorporated in these diets.

Prior studies have shown that healthy lifestyle bias may confound the observed association between ASF consumption and CVD or other diseases. Thus, the current study aimed to analyze the contribution of multiple sample characteristics and health behaviors to the association between ASF intake and CVD.

In many observational studies, ASF-eaters were more likely to have more disease risk factors or unhealthy characteristics.”

What did the study show?

The current study cohort comprised a representative sample of over 20,000 Americans. All data were obtained from the National Health and Nutrition Examination Survey (NHANES) 2013-2016.

Overall, about 5% of the study cohort had CVD. Males had a higher mean food intake, higher serum lipids in all categories except high-density lipoprotein (HDL) and total cholesterol, higher proportional ASF intake, and more physical activity than females.

Individuals with CVD were twice or more as old as other participants. Additionally, these individuals were heavier, less active, had higher lipid levels, smoked more cigarettes every day, and consumed more ASFs.

About 70% of the youngest participants' diets consisted of ASFs. These diets were also associated with the lowest energy intake and lowest serum cholesterol levels, except for triglycerides. Nevertheless, this group reported the most exercise or physical activity and the highest ratio of total to HDL cholesterol.

In the unhealthy group, study participants were in the oldest age group, with high energy intake, years on medication, and low-density lipoprotein (LDL) levels. Conversely, these individuals' total cholesterol and HDL were low, with many having lower incomes and consuming less fiber.

Approximately 60% of participants who consumed red meat had a history of CVD as compared to only 23% for white meat. Those who ate processed meat had a lower prevalence of CVD at 15%.

Individuals who consumed red meat were older, had more CVD conditions, lower HDL, higher LDL, and smoked more. However, these individuals had fewer disease years than those who ate processed or white meat.

Age, a history of smoking, body mass index (BMI), lipid profile, and socio-economic and ethnicity were individually associated with CVD risk. Specifically, over 75% of the CVD risk was attributed to certain factors, including obesity, lack of adequate physical activity, smoking, low fiber intake, neglect of healthcare, and age above 60 years.

About 25% of participants 60 years or older had CVD, which is comparable to less than 10% and 1% of those between 50-59 years and 20-29 years of age, respectively, with this condition. Blacks and non-Hispanic Whites were at a greater risk of CVDs than Whites at 6%.

Although males with CVD were more physically active and had lower lipids in several categories, including TC and LDL, they had more CVD conditions and lower HDL than females of the same age. The lower lipid levels may reflect their use of lipid-lowering or other medications aimed at improving metabolic markers, while higher alcohol consumption among males could explain the lower HDL and more elevated triglycerides. Insufficient physical activity was more prominently linked to increasing CVD risk in males, perhaps because of lifestyle changes.

When three or more of these factors were present, the risk of CVD was observed in about 75% of prevalent cases. Conversely, the absence of three or more factors was associated with a low CVD risk in 70% of cases.

The likelihood that the participant would have CVD increased with every 90-minute increase in moderate physical activity; however, this association was only observed after adjusting for sex. This may be attributed to males often initiating treatment only after a relatively long period of latent or advanced CVD.

Males were first diagnosed with CVD at a mean of 10 years after the point when their risk began to rise at 45 years. Comparatively, the corresponding diagnosis in females was made at a mean age of 54 years and before the point of increasing risk at 55 years.

Even in participants who reported changes towards healthy lifestyles, several modifiable risk factors, such as obesity, higher triglycerides, and lower HDL levels in those with a history of CVD, were observed. This was despite almost two-thirds of these individuals reporting that they had received advice from their doctors about lifestyle changes, primarily about more physical activity and dietary modifications.

Study participants who reported healthy lifestyles were more likely to have been diagnosed with CVD earlier as compared to those with unhealthy behaviors.

What are the implications?

The study findings indicate that researchers should explore more than dietary or lifestyle factors alone when assessing associations with CVD risk. Demographics such as sex, income, and educational level contribute to compliance to health behavior counseling, which agrees with earlier reports. Other obstacles like poor training, limited time, and poor remuneration also prevent effective counseling on lifestyle changes by physicians and other clinical workers.

It appears red meat consumption but not overall ASF consumption is a plausible surrogate for an unhealthy lifestyle and that certain risk factors remain prevalent in those with CVD, despite evidence of lifestyle change.”