High-protein diet linked to heart failure in older women

 Women older than 50 who eat high-protein diets could have a greater risk of heart failure, especially if a lot of their protein comes from meat, according to a new study presented at the annual scientific conference of the American Heart Association.

Researchers found that postmenopausal women who follow a high-protein diet had a significantly higher rate of heart failure than those who ate less protein daily or ate more vegetable protein.

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The study examined the dietary protein intake of 103,878 women, ages 50 to 79, from 1993 to 1998. They self-reported their daily diets, which researchers noted can be unreliable; researchers also used biomarker data to determine actual amounts of dietary protein. Although all participants were free of heart failure during that period, about 1,700 of them developed heart failure by 2005.

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Researchers adjusted for age, education, race or ethnicity and heart failure risk factors such as high blood pressure, diabetes, coronary artery disease, anemia or atrial fibrillation.

"We found that by increasing the total dietary protein intake, there was a statically significant increase in the incidence of heart failure," said Dr. Mohamad Barbour, an internist at the Alpert Medical School of Brown University, Memorial Hospital of Rhode Island and lead author of the study.

In fact, the risk was almost double.

Meanwhile, women whose proteins were sourced mainly from vegetables appeared to be at a lower risk of heart failure.

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This could be attributed to the molecular mechanisms of animal protein, Barbour said, explaining that animal proteins can turn to toxic molecules, which can in turn affect the function of the heart's left ventricle and lead to heart failure. They can also increase the body mass index, a known risk factor for heart failure.

"Our study should be interpreted with caution," warned Barbour. "It appears that a high-protein diet may increase the risk of heart failure among postmenopausal women; however, more research will be needed."

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Dr. Mingyang Song, a researcher at Massachusetts General Hospital and the Harvard T.H. Chan School of Public Health, described the findings as interesting. Song was the lead author of research published this year that found replacing animal protein with plant protein in a person's diet was associated with a decreased risk of death. He was not involved in the new research.

"People who eat high vegetable proteins may also have a healthier lifestyle," Song said. This may imply that other factors are responsible for lowering the risk of heart failure for that group, he added.

"I think it'll be good to replicate the results in other studies," he said, suggesting that a more controlled group with a more controlled food intake could be required for that purpose.

 

A number of studies have suggested a diet high in protein can aid weight loss. Now, researchers have shed light on the underlying mechanisms of this association, which may open the door to new preventive and treatment strategies for obesity.

Researchers have learned more about how protein-rich foods affect appetite and weight.

In a new pilot study, researchers from Imperial College London in the United Kingdom reveal how phenylalanine - an amino acid produced by the digestion of protein - boosts levels of a hormone that tells us when we are full, leading to reduced food intake.
Lead author Mariana Norton will present the findings at this week's Society for Endocrinology annual meeting in the U.K.
Previous studies have shown that a diet high in protein - essential nutrients found in foods such as milk, fish, eggs, and poultry - can help reduce body weight by suppressing appetite.
According to Norton and her team, a high-protein diet can be hard to adhere to, but uncovering the mechanisms by which protein curbs hunger could lead to simpler weight-loss strategies.

How phenylalanine leads to weight loss

For their study, the researchers conducted a series of experiments on rodents, which involved testing the effects of phenylalanine.
Phenylalanine is an amino acid produced in the gut after consumption of foods rich in protein.
Firstly, the team gave 10 mice and rats a single dose of phenylalanine and compared them with rodents that were not given the enzyme.
The researchers found that mice and rats given phenylalanine showed increased levels of the hormone GLP-1, which suppresses appetite, but reduced levels of the hormone ghrelin, which increases hunger.
Additionally, the researchers found that phenylalanine reduced the rodents' food intake and increased weight loss. Rats that received the amino acid also moved around more, which the team notes may have contributed to their weight loss.
Next, the team administered regular doses of phenylalanine to mice with diet-induced obesity over a 7-day period.
Compared with mice that were not treated with phenylalanine, those that received the amino acid showed a reduction in weight, the researchers report.

Phenylalanine stimulates CaSR receptor to reduce appetite

In a final experiment, the researchers sought to gain a better understanding of the mechanisms by which phenylalanine affects levels of GLP-1 and ghrelin.
On applying phenylalanine to gut cells in a petri dish, the team found that the amino acid targets a receptor called the calcium-sensing receptor (CaSR), and it is this receptor that increases GLP-1 levels and lowers levels of ghrelin.
Obesity has become a major public health concern in the United States; around 2 in 3 adults and 1 in 6 children and adolescents are considered obese, putting them at greater risk of health conditions such as diabetes, heart disease, and some types of cancer.
According to Norton and her team, their findings may fuel much-needed new strategies to tackle the obesity epidemic.

"Our work is the first to demonstrate that activating CaSR can suppress appetite. It highlights the potential use of phenylalanine or other molecules which stimulate CaSR - like drugs or food components - to prevent or treat obesity."

Mariana Norton

The researchers note that further studies are needed to pinpoint the exact mechanisms by which phenylalanine can curb hunger and aid weight loss, and future research should assess whether the amino acid poses the same appetite-suppressing effects in humans as in rodents.
Read how a week's overeating could be counteracted by exercise.

Written by Honor Whiteman