Protein proportion is key to weight loss
If people eat the correct proportion of high-quality protein, their carbohydrate, fat and overall energy intake will take care of itself.
This is the hypothesis of 2 Sydney professors who believe it has the potential to change the way doctors treat obesity.
Too low a proportion of protein in the diet makes people gain weight because they over-compensate with fats and carbohydrates to get enough protein. Too high a proportion of protein will help them lose weight, but is also likely to speed up ageing and increase the risk of late-life disease, especially when coupled with low proportions of healthy carbohydrates.
That’s the essence of what professors Stephen Simpson and David Raubenheimer have named the protein leverage hypothesis.
Good nutrition, they say, is all about the balance between macronutrients (fat, protein and carbohydrates) in the diet. And key to that balance is the ratio of protein to carbohydrates and fats.
“That is the big theme,” says Prof Simpson, the academic director of the Charles Perkins Centre, Sydney University’s $500 million investment in finding a way to ease the burden of obesity, diabetes and cardiovascular disease.
For humans, the key issue is appetite, he says. “If you have a low proportion of protein in your diet, the characteristics of the human appetite are such that this will lead us to overeat fats and carbs.”
The midpoint of the current Australian dietary guideline of 15-25% of energy from protein is about right on a population level. But the challenge is to tailor the proportions according to life-stage, genetic makeup, ethnicity and personal health.
The professors are reluctant to put exact figures to their hypothesis at this stage. But the evidence is suggesting that for pregnant mothers it is best for about 20% of energy to come from high-quality protein coupled with healthy carbohydrates and modest amounts of healthy fats.
In late middle age it’s looking as if a lower proportion of protein coupled with healthy carbohydrates is a healthier diet in terms of metabolic outcomes than one that is high in protein and low in carbohydrate.
“We also know that if you are obese and wish to lose weight, then in the short term a high-protein diet, say 25%, is a good way to go,” says Prof Simpson.
These three meals shown are intended to illustrate what 20% of protein looks like in practical terms. They provide about 7000kJ with 85g protein in total, which would be lower than the recommended energy requirements for many adults. Another meal could be included or the menus could be adjusted for individuals with different energy requirements by increasing(or decreasing) the amount of every food in each meal by the same multiple (ie. 1.5 x each food would give 1.5 x energy but maintain the proportions of protein, fats and carbohydrates). NOTE: These are example meals and do not reflect a whole days intake for all