Dietary sources of protein include cheese, eggs (particularly egg whites), fish and lean beef.
"We've shown that when compared head-to-head, mice got the same benefits from a low protein, high carbohydrate diet as a 40% caloric restriction diet," says Prof. Stephen Simpson, senior author of the study and Academic Director of the University of Sydney's Charles Perkins Centre in Australia.
According to the study authors, reducing the amount of calories consumed by around 30-50% increases health span, delays the onset of age-associated diseases and improves metabolic health. Unfortunately, this level of caloric reduction is unsustainable for most humans.
"Except for the fanatical few, no one can maintain a 40% caloric reduction in the long term," says Prof. Simpson, "and doing so can risk loss of bone mass, libido, and fertility."
Additionally, other studies have indicated that when animals have unrestricted access to food, caloric reduction (through dietary dilution) did not improve lifespan. Conversely, in such situations, diets low in protein and high in carbohydrates were found to improve lifespan and metabolic health in later life.
These findings suggest that a low protein, high carbohydrate diet could be a more feasible dietary intervention for humans than caloric reduction although previous research has also found an associated risk of increased food intake with this diet.
To investigate which dietary intervention is most effective at improving metabolic health, the researchers compared three different diets with varying protein-to-carbohydrate ratios:
- High protein, low carbohydrates
- Medium protein, medium carbohydrates
- Low protein, high carbohydrates.
The researchers tested each diet for 8 weeks twice; once under conditions where calories were restricted and once where food was freely available.
'Modest protein intake with plenty of carbohydrates is beneficial' according to authors
Mice that followed a low protein, high carbohydrate diet where food was always available derived the same benefits as mice following the same diet where the number of calories consumed was restricted. Improvements relating to blood sugar, cholesterol and insulin levels were recorded even with increased food consumption.
Despite increased consumption when food was freely available, mice following a low protein, high carbohydrate diet also had higher metabolism than mice on the calorie-restricted diet without gaining extra weight. No extra benefits were observed in the mice following the low protein, high carbohydrate diet with caloric restriction.
The study, published in Cell Reports, is an observational one and so further work will be required investigating the mechanisms behind these findings. Currently, the researchers do not know precisely how the type and quality of proteins and carbohydrates consumed affect metabolic health and long-term survival.
"An important next step will be to determine exactly how specific amino acids, the building blocks of proteins, contribute to overall health span and lifespan," says lead author Dr. Samantha Solon-Biet, also of the University of Sydney.
The researchers also do not know whether these findings apply to humans as well as mice. If they do, it means that adjusting the quantities of carbohydrates and protein consumed could be a more realistic approach for improving metabolic health and reducing the risk of certain chronic diseases than cutting calories.
"According to these mouse data and emerging human research, it appears that including modest intakes of high-quality protein and plenty of healthy carbohydrates in the diet will be beneficial for health as we age," Prof. Simpson concludes.
Last month, Medical News Today reported on a review examining the causes of obesity. The authors state that excess sugar and carbohydrates, not a lack of exercise, are to blame for the obesity epidemic.