Experts say protein in foods such as eggs and meat are necessary for overall health, but people should be careful not to consume too much on a daily basis.
- Researchers report that
taking in too much protein on a daily basis can produce heart health
issues.
- In particular, they
note, consuming more than 22% of daily calories from protein can increase
the risk of atherosclerosis.
- Experts say some daily protein is necessary to maintain good overall health, but they advise that some of that protein should come from plant-based foods.
Consuming more than 22% of daily
calories through proteins may increase the risk of atherosclerosis and even
worsen the condition, according to a study completed
at the University of Pittsburgh and published today in the journal Nature Metabolism.
To reach their conclusions, the
researchers used human trials along with experiments involving mice and cells
in Petri dishes. The human studies had a total of 23 participants.
Researchers used two different study
set-ups for the human studies. Both involved asking participants to have
two liquid meals –
one with standard protein and
one with high protein – about one to two weeks apart.
The first set-up involved 14
participants. The standard meal had 10% of total energy as protein, 17%
as fat,
and 73% as carbohydrates.
The high protein meal consisted of 50% of energy from protein, 17% as fat, and
33% carbohydrates.
The second setup involved nine
participants and was designed to mimic a “real-world” scenario. In this setup,
the standard meal was representative of a person’s average protein intake and
had 15% of total energy as protein, 35% as fat, and 50% as carbohydrates. The high
protein meal represented the upper quartile of protein intake and consisted of
22% of energy from protein, 30% as fat, and 48% carbohydrates.
The scientists noted that leucine is
an amino acid that
contributes to the development and worsening of atherosclerosis.
They found that higher dietary protein intake, specifically intake of more than
25 grams of protein per meal or 22% of daily energy requirements, led to higher
leucine levels that activated a specific pathway in immune cells that is
associated with atherosclerosis.
The second part of the study involved
mice.
The researchers first created diets
for the mice with graded protein contents that mimicked the average (15%) and
high (22%) protein intake for a typical adult living in the United States.
They reported similar results to the
human studies.
They added that the same pathway was
activated in mice receiving more than 25 grams of protein per meal, or 22% of
total energy intake, and that these mice were also more likely to promote
atherosclerosis and cardiovascular disease.
Conclusions
from the protein diet and atherosclerosis study
The researchers conclude that high
protein intake can contribute to atherogenesis.
The authors suggest that people
approach high protein
diets cautiously and that dietary guidelines are revised
accordingly.
The authors note the recommendation
from several organizations is that protein intake be about 11% of daily energy
requirements to maintain nitrogen balance.
“High protein diets are very popular
with the public, used for weight loss, bodybuilding,
and an overall healthy lifestyle. For many years, reports in the research world
using experiments in animal models showed that high protein diets can increase cardiovascular disease (also
called atherosclerosis or hardening of the heart arteries), but no one knew
why,” said Dr. Babak Razani, a professor of medicine at the University of
Pittsburgh and one of the authors of the study. “In our previous 2020 paper,
we used mouse models to define the mechanism for this by showing that protein
ingestion activates macrophages,
an immune cell that is a key driver of atherosclerosis, and we identified an
important protein in the macrophages called mTOR that mediates this process.”
“Now, in the current study, we pin
down the reasons why high protein diets are risky for our heart arteries,”
Razani told Medical
News Today. “First,
we did several studies in humans to demonstrate that when people eat higher
amounts of protein, our macrophages and the mTOR pathway get activated just
like we found in animal models. Then, we identified, for the first time ever,
the role of leucine – an amino acid highly enriched in animal-based proteins –
as the driving force of atherosclerosis risk. Amino acids are the building
blocks of proteins and there are 20 of them that make up any protein we ingest.
But it is only leucine that is the bad actor in worsening the heart artery
disease. We determined that eating meals containing about 22 percent
kilocalories of protein is the threshold at which the protein and its leucine
elevate risk.”
Differing
opinions on daily protein intake
Two studies, one published in 2020
and one in 2023 came to different conclusions.
The first study, published in
2020, is the previous study by Razani and his colleagues that
reported that high protein diets increase risk of cardiovascular disease.
The study
published in 2023 found no statistical difference in
cardiovascular outcomes between standard and high protein diets.
Even so, some cardiologists say they
are moving away from recommending high protein diets and suggesting more
plant-based and vegetable-based diets.
“This [new] study is too small to
change anything,” said Dr. Stephen
Tang, a cardiac electrophysiologist at Providence Saint John’s
Health Center in California who was not involved in the research.
“I would not do anything different,”
Tang told Medical
News Today.
“However, it does provide more evidence that high protein is not the way to go.
Cardiologists are traditionally focused on cholesterol and high blood pressure –
not protein. This study confirms that a plant-based diet is good for heart
health.”
Advice
about protein from dietitians
So, how much protein should included
in a daily diet? How much is too much?
“While the results of the study are
interesting, they don’t exactly reflect real world examples of over-consuming
protein,” said Caroline
Thomason, RD, CDCES, a dietitian based in Washington, D.C., who was
not involved in the latest research.
“While it’s true that most western
societies over-eat protein and under-eat nutrient dense plant-based foods like
fruits, vegetables, and whole grains, protein as a food group is inherently
satiating and quite hard to over-eat, especially in the context of a balanced
diet,” Thomason told Medical
News Today.
Another expert said there are ways to
understand how this type of information can translate into everyday life.
“Whenever you eat excessive amounts
of one nutrient, you end up limiting others, which can potentially cause health
problems,” said Anne Danahy, RDN, a registered dietician nutritionist
practicing in Arizona who was not involved in the latest research. “There’s
good reason for the saying ‘everything in moderation.’ A healthy diet should
provide balanced amounts of protein, fat, carbs, vitamins, and minerals.”
“Everyone’s protein needs are
slightly different, so it’s best to talk to a dietitian who can assess your
needs,” Danahy told Medical
News Today.
“However, I find for most healthy adults, a good goal is 20 to 30 grams of
protein per meal, spread out evenly throughout the day.”
“Protein intake that exceeds this may
not be used for muscle synthesis. It often ends up providing excess calories,
and as this study suggests, it may cause more harm than good,” she added.
Danahy recommends eating more plant protein (from
foods instead of supplements) for anyone looking to add extra protein to their
diet.
“Several studies have associated
high animal
protein diets with an increased risk of cardiovascular
disease,” she said. “Protein from animal sources may also contain saturated fats or
other compounds that can boost inflammation and
promote heart disease.”
“On the other hand, protein supplied
by plant sources contains antioxidants, fiber, and
other nutrients that can reduce the risk of heart disease,” Danahy concluded. “Nuts, seeds,
legumes, and vegetables all contain protein and other
health-promoting compounds.”
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