The protein trap: it might make you lean, but will it make you live longer? Photo: craftvisionToo much saturated fat will clog your arteries, too much sugar will give you tooth decay, and both are to blame for your bulging waistline. Protein may keep you lean but not long-lived. And calories, oh well, you should definitely cut down on those if you want to live to an old age.
The advice and warnings surrounding diet and nutrition are so constant and often so contradictory it is hard to know what to believe.
Should you follow the Atkins diet for lean muscles or fast for two days on the 5:2 diet to improve your brain function? Should you quit sugar or fat or both?
These mixed messages stem, in part, from the methods scientists have used for decades to study the effect of nutrition on our health. For years research has primarily focused on the individual components of our diet – the protein, the fat, the carbohydrate or the total number of calories we consume – and their impact on obesity, ageing and other aspects of health.
What has been missing from this approach is how nutrients interact with each other to influence our wellbeing.
”By definition, diet is a multi-dimensional thing”, says Steve Simpson, a biologist from the University of Sydney. ”We require dozens of different nutrients each in their appropriate amounts and balance if we’re to be happy and healthy.”
For the past decade, Simpson and others have led the world in a new approach to analyse the relationship between diet, weight gain and other health problems such as diabetes and heart disease.
Central to their thesis is the idea that it is the ratio of protein to fat to carbohydrates not just the individual nutrient that matters. This month they published the most compelling evidence to date that found, in mice, different nutrient ratios had profoundly different impacts on the body.
For instance, mice on high-protein, low-carbohydrate diets had reduced body fat and consumed less food overall, but the trade-off was they had shorter lifespans and poor heart health.
Another group of mice that consumed a high-carbohydrate, low-protein diet were slightly rounder from an increase in body fat – up to 10 per cent more than high-protein diet mice – but they lived longer and had fewer age-related health problems.
Mice on low protein, high fat diets fared the worst and died youngest.
”This is illustrative of how important it is to take account of the balance of nutrients,” says Simpson, the director of the Charles Perkins Centre.
The mice study, which was published in the journal Cell Metabolism, supports earlier findings the group made in flies and is consistent with research in humans – increasing the proportion of protein in the diet will lead to weight loss.
“If that’s really what matters for your health then the fact that over the long term this may cause chronic problem may be less critical,” he says.
The team is still investigating why high amounts of protein shorten the life of mice, but they suspect one component, branched-chain amino acids, play an important role. Simpson’s collaborator, geriatric medicine researcher David Le Couteur, says the mice fed high carbohydrate/low protein meals had lower levels of these compounds circulating their body and lived about 50 weeks longer than high protein rodents.
”Branched-chain amino acids are good for building your muscles but at the cost of late life health,” he says.
Mark Febbraio, a diabetes researcher from Baker IDI in Melbourne, says the evidence on the relationship between protein intake, body weight and a shorter lifespan, gathered from many species, is compelling. “Weight loss is not always the be all and end all.”
The findings have helped counter the claims of some popular diets with little scientific basis including the ”paleo diet” where followers are encouraged to eat mostly fish, meat and vegetables like our hunter-gatherer ancestors, eschewing grains and dairy.
“There’s this massive paleo movement which advocates a high fat, low carb diet. It results in weight loss but whether it’s a healthy diet is another thing,” says Febbraio.
Simpson is quick to point out that the body of any species has different nutritional needs at different times of its life. While lots of protein shortened life span in some animals, the nutrient is critical for growth, repair and in pregnancy, he says.
So how does an animal’s body ensure its owner eats the right balance of nutrients at the right time?
What drives an animal’s internal appetite has been a major interest for Simpson and his team.
“If you think about it logically the body is constantly making decisions about what to eat and when,” he says.
It does this by taking into account what it needs, combining that information with the nutrients already circulating the body or stored in fat, muscles and other tissues. To encourage an animal to eat what the body needs, sophisticated internal appetite systems have evolved for each major nutrient – protein, fat and carbohydrates.
”The body doesn’t just mash it all up and count calories, it makes separate decisions and integrates them in the brain,” says Simpson.
Investigations on a range of species such as slime mould, insects, fish and mice have shown that most organisms have the capacity to make separate decisions about which nutrient it needs over others. Time and time again, they find the dominant appetite is protein, making it the major driver of an animals’ total food intake.
When mice reached a certain protein target they would stop eating, says Le Couteur. ”If they didn’t have enough protein they would overeat,” he says.
After protein, the mice’s internal appetite favoured carbohydrates, followed by fat. While Simpson acknowledges that mice are not people, overeating on a low protein diet has been documented in human clinical trials and surveys.
But if humans, like other species, have a biological imperative to eat a nutritionally balanced diet, principally driven by an appetite for protein, why are so many people overweight?
Simpson suspects the answer may come from our early ancestral environment, where simple sugars and fats were rare. Their scarcity would have made them highly desirable to early humans, he says.
But in a world where fatty, energy dense food is cheap and plentiful it is easy to over-indulge, especially if a person doesn’t eat enough protein to satisfy their body’s needs.
”Our physiology hasn’t kept up with the rate of change of our environment,” says Simpson.
This story Administrator ready to work first appeared on Nanjing Night Net.
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