- There is much debate about the role of dietary cholesterol in people’s health.
- An increasing number of studies into dietary cholesterol have funding from the food industry.
- A new review identifies an association between studies with food industry funding and more favorable interpretations of the role of egg cholesterol in human health.
In a systematic review, researchers looked at how authors of industry- and non-industry-funded studies interpret the results of research on egg consumption and blood cholesterol levels.
The study, which appears in the American Journal of Lifestyle Medicine, found that the authors behind studies funded by industry were more likely to interpret results regarding the relationship between egg consumption and cholesterol favorably — and often not in line with what the data suggested.
In the past, scientists have recommended that people consume under 300 milligrams (mg) of cholesterol each day to maintain good cardiovascular health.
However, more recent research has not found a significant relationship between dietary cholesterol and the risk of cardiovascular disease.
As a consequence, recent guidelines from the American Heart Association (AHA) and the American College of Cardiology have not specified a target for daily dietary cholesterol intake.
Nonetheless, there has been “intense debate” regarding the role that consuming eggs might play in increasing blood cholesterol levels. On the one hand, eggs are a major source of dietary cholesterol. On the other, they are a cheap, nutritious, and widely available food item.
In the recent study, the researchers wanted to understand how funding sources for research into egg consumption and blood cholesterol levels have changed over time.
They also wanted to know whether or not the source of funding for studies — that is, either industry or non-industry — made a difference in how researchers interpreted the results.
The researchers searched databases for articles involving adults that studied egg or egg yolk consumption and total or low-density lipoprotein cholesterol.
They identified 211 studies published between 1950 and 2019 that met these inclusion criteria.
The researchers found that industry-funded research into egg consumption and cholesterol increased from 0% of cholesterol studies in the 1950s to 60% of these studies in the 2010s.
The majority of the studies found that egg consumption did increase blood cholesterol concentrations.
However, the authors of the review found that 49% of the studies funded by industry did not accurately interpret their findings, being more likely to suggest a neutral or positive relationship between egg consumption and blood cholesterol concentrations. This compares with 13% of the studies not funded by industry.
Micro B Life spoke with corresponding study author Dr. Neal Barnard, an adjunct professor of medicine at the George Washington University School of Medicine. Dr. Barnard is also the president of the Physicians Committee for Responsible Medicine (PCRM).
He said: “The egg industry has a huge financial interest in making eggs seem healthy. So, industry-funded researchers have tried to downplay eggs’ cholesterol-raising effect. They have not really succeeded, though: Even their own studies show that eggs raise cholesterol.”
Dr. Barnard said that industry funding was not necessarily the problem — rather, the problem is when pressures from industry result in interpretations that do not reflect the findings.
“It’s understandable that the food industry would want to do research studies on its products. That’s OK. The problem arises when it tries to bury unfavorable findings.”
“We’ve seen this repeatedly, especially with the egg, dairy, and meat industries, because they are trying to rehabilitate a tarnished image related to cholesterol and other risks. They are hoping to make these issues go away.”
– Dr. Neal Barnard
Other factors at play?
Dr. Christopher Gardner — the Rehnborg Farquhar Professor of Medicine at the Stanford Prevention Research Center of Stanford University in California and an expert on the potential health benefits of various dietary components or food patterns — also spoke with MBL.
He explained that the findings were unsurprising but cautioned that there might be other factors that explain the results.
Dr. Gardner pointed out that while eggs contain a significant amount of cholesterol — around 200 mg per egg — the body excretes half of the cholesterol that a person consumes. The average person in the United States consumes around 300 mg of cholesterol in their diet each day. The body excretes half of this cholesterol and retains the other half.
The liver naturally produces 1,000 mg of cholesterol each day. Cholesterol is essential for building cell membranes.
However, as Dr. Gardner explained to MBL, the liver produces less cholesterol to account for any cholesterol that a person consumes.
As an example, he explained that if someone eats 300 mg of cholesterol from eggs or other sources, the body absorbs 150 mg and sends it to the liver. The liver, instead of making 1,000 mg, makes 850 mg. So, overall, the body still has 1,000 mg, and “the net impact in the blood would be no change.”
Instead of dietary cholesterol, Dr. Gardner said that saturated fat is more likely to increase concentrations of cholesterol in the blood.
Furthermore, Dr. Gardner said that the following factors could all complicate a straightforward conclusion of whether or not egg consumption is linked to increases in blood cholesterol concentration:
- number of participants
- study duration
- characteristics of the participants
- amount of cholesterol consumed
- level of adherence to the study diet
- amount of saturated fat consumed
“Let’s say there are two new studies, one funded by industry and one funded by PCRM. Is it possible that under one set of conditions, the dietary cholesterol did, and in another set of conditions did not raise blood cholesterol?”
“To answer the question about whether one group is lying (or misinterpreting), one would have to go through all of the possible differences between the two studies. One of those differences would be, ‘Was it funded by industry or by PCRM?’”
“Simplistically, both studies were done to test if dietary cholesterol raises blood cholesterol. One study concludes: ‘Yes,’ dietary cholesterol caused blood cholesterol to rise. The other study concludes ‘No.’”
“It is possible for both studies to be interpreting their findings correctly. The different conclusions would be due to differences in study design and implementation.”
Dr. Gardner said that unconscious bias could also be a factor that could affect the conclusions that researchers draw.
“Is it possible that some of the subtle nuances in all of this could be manipulated in such a way as ‘not to lie’ but to ‘be misleading’ about the findings? Yes! If you read Marion Nestle’s book Unsavory Truth: How Food Companies Skew the Science of What We Eat, you’ll find that she talks a lot about ‘unconscious bias.’”
“This refers to the lack of conscious intent to be misleading, but falling prey to setting up the study in such a way as to make it more likely that a desirable conclusion is reached while convincing yourself that the study design is objective and appropriate.”
– Dr. Christopher Gardner
“That is one way to explain how the findings of a study could be misinterpreted.”
Dr. Gardner said that, ideally, nutrition research should be funded by bodies such as the National Institutes of Health (NIH), who do not have conflicts of interest. However, the sheer cost of running studies means that this is prohibitive.
“If you combined the money from the [NIH], the U.S. Department of Agriculture, [the National Science Foundation] International, the [AHA], the World Health Organization [WHO], and others, there wouldn’t be enough funding to address all of the common — and practical — questions that the public has about food and health.”
“So, who would fund such studies? Turns out the egg board will fund cholesterol studies, the blueberry industry will fund antioxidant studies, the dairy industry will fund bone fracture studies, and so on.”
“How could we appropriately fund nutrition studies? Take all of the healthcare money spent treating heart disease, diabetes, stroke, and cancer, and all of the military budget and the space budget, and put it toward nutrition studies. That would help a lot!”
“What seems a crime to me,” Dr. Gander continued, “is how much of our research money goes to drug and device treatment for the diseases caused by poor diets. The proportion of money that goes to nutrition research is shockingly low — something on the order of 1/100th of the money that goes to drugs and devices.”
“Good nutrition could prevent many downstream issues. But that would mean looking at the long-term picture, and that doesn’t work well when the quarterly report earnings need to show profits.”
– Dr. Christopher Gardner
Whole food plant-based diets
Drs. Barnard and Gardner both said that a diet that focuses on fruits, vegetables, and whole grains promotes health.
“Luckily, some debates have been settled, and there is no controversy: Vegetables are good for you. So are fruits, whole grains, and everything in the bean group: beans, peas, lentils, etc. The science is clear, and there is no debate there,” said Dr. Barnard.
“Where the debate comes in is with commercial products containing ‘bad’ fat, cholesterol, and untoward amounts of sugar. So, meat, dairy products, eggs, coconut and palm oil, and sodas will continue to be part of a tug-o-war between industry and health advocates.”
Dr. Gardner said that “[t]he advice of the [AHA] is to think less about specific nutrients — such as cholesterol — and more about overall food patterns.”
“If one follows a healthy Mediterranean-style diet, the foods involved in that pattern tend to be low in dietary cholesterol without mentioning it. They tend to be low in saturated fat without mentioning it. They tend to be high in fiber without mentioning it. And the overall ‘pattern’ has been shown again and again, in different ways, to be [healthy].”
“Another way to frame this is as a whole food plant-based (WFPB) diet, which is very similar to a Mediterranean diet. After all, people don’t shop for nutrients; they shop for foods,” said Dr. Gardner.
“Shopping for the foods that would go into a Mediterranean diet (or a WFPB diet) would involve lots of veggies, beans, nuts and seeds, fruits, whole intact grains, and modest amounts of fish, yogurt, eggs, and some other animal products.”
“It would mean avoiding added sugars and large dessert portions of refined fats and grains. This is the approach that is being taken by the