Reduced-calorie diet slows ageing in humans
A study of people who reduced the calories they consumed has found the strongest evidence yet that such restrictions can slow down human metabolism.
The results raise hopes that a low-calorie lifestyle — or treatments that mimic the biological effects of restricted eating — could prolong health in old age and even extend life.
Past work in many short-lived animals, including worms, flies and mice, has shown that calorie restrictions reduce metabolism and extend lifespan. But experiments in longer-living humans and other primates are more difficult to conduct and have not yet drawn clear conclusions.
The study was part of the multi-center trial called CALERIE (Comprehensive Assessment of Long term Effects of Reducing Intake of Energy), sponsored by the US National Institutes of Health.
The randomized, controlled trial tested the effects of two years of caloric restriction on metabolism in more than 200 healthy, non-obese adults.
“The CALERIE trial has been important in addressing the question of whether the pace of ageing can be altered in humans,” says Rozalyn Anderson, who studies ageing at the University of Wisconsin–Madison.
She leads one of two large, independent studies on calorie restriction in rhesus monkeys, and began her research career studying calorie restriction in yeast. “This new report provides the most robust evidence to date that everything we have learnt in other animals can be applied to ourselves.”
Published on 22 March in Cell Metabolism, the latest study looked at 53 CALERIE participants who had been recruited at the Pennington Biomedical Research Center in Baton Rouge, Louisiana.
This facility is home to four of the world’s 20 or so state-of-the-art metabolic chambers, which are like small, sealed hotel rooms that measure minute-by-minute the amount of oxygen that occupants use and how much carbon dioxide they exhale.
This allows researchers to track how the occupants use energy with unprecedented precision, says Anderson.
The ratio between the two gases, combined with analysis of nitrogen in occupants’ urine, indicates whether the occupant is burning fat, carbohydrate or protein.
The trial participants, aged between 21 and 50, were randomized into two groups: 34 people in a test group reduced their calorie intake by an average of 15 per cent, and 19 people in a control group ate as usual.
At the end of each of the two years, they all underwent a range of tests related to overall metabolism and biological markers of ageing, including damage associated with oxygen free radicals released during metabolism. They were also placed in the metabolic chamber for 24 hours.
The scientists found that participants on the diet used energy much more efficiently while sleeping than did the control group.
This reduction in their base metabolic rate was greater than would be expected as a result of the test group’s weight loss, which averaged nearly 9 kilograms per participant.
All the other clinical measurements were in line with reduced metabolic rate, and indicated a decrease in damage due to ageing.
Also, the verdict is out: Grilled and well-done food raise blood pressure by 17 per cent. We know red meat is not the best thing for your blood pressure, and fish or chicken would be a ‘leaner’ option at a barbecue.
But a new Harvard study warns that they are all as bad as each other when grilled.
The alarming new research, released just months before cook-out season begins, found grilling meat triggers the release of dangerous chemicals that inflame the arteries and increase hypertension risk by 17 percent.
While the study could not prove a direct cause-and-effect, they said the link is strong enough to warn people to think twice about getting their meat well-done and grilled, and to consider rare, raw or boiled dishes more often.
To assess the link, researchers at the Harvard T.H. Chan School of Public Health, United States, assessed data on tens of thousands of medics from nationally-representative surveys.
First, they analyzed 32,925 in the Nurses’ Health Study, then 53,852 women in the follow-up to that study. Lastly, they assessed 17,104 men from the Health Professionals Follow-Up Study.
Each study recorded everything from diet to sleep to mood and daily habits.
The research team focused on food, cooking methods and blood pressure.
At the start, none of the people in the various surveys had high blood pressure, diabetes, heart disease, or cancer.
However, by the 12-year follow-up, 37,123 people had developed hypertension.
Taking a closer look, the researchers spotted a clear link between higher hypertension risk and cooking method, rather than foods alone.
While most people involved in the survey reported eating at least two servings of red meat, chicken or fish per week, their risk varied depending on how those dishes were cooked.
Their risk was 17 percent higher if they ate grilled or roasted beef, chicken or fish more than 15 times a month, compared with those who indulged in grilled meals fewer than four times a month.
Those who prefer well-done meats had a 15 percent higher risk of hypertension compared to people who go for rarer plates.
This was the case regardless of how much meat they ate, or what the dish was.
“The chemicals produced by cooking meats at high temperatures induce oxidative stress, inflammation and insulin resistance in animal studies, and these pathways may also lead to an elevated risk of developing high blood pressure,” said lead author Dr. Gang Liu, a postdoctoral research fellow of nutrition.