University of Arizona Study Shows Moderate Calorie-Restricted Diet Improves Metabolism and Physical Function

Key Points

• Beginning a reduced-calorie diet at a young age improves lean muscle mass throughout the lifespan.
• Modest calorie intake reduction improves insulin resistance, a risk factor for type II diabetes.
• A lifelong moderate calorie-restricted diet improves physical function as measured with grip strength.

Residents of Okinawa consume, on average, 11% fewer calories than others around the world, have lower body fat, and exhibit reduced mortality from age-related diseases. Although these tantalizing data show a correlation between reducing calorie intake and healthier aging, they don’t establish a causal link. Furthermore, most animal studies showing that caloric restriction prolongs lifespan apply somewhere between a 30% to 40% reduction in caloric intake, which most people can’t maintain. As such, we’ve lacked research testing humanly feasible levels of caloric restriction, which may not prolong lifespan but extend the number of years lived in good health – our healthspan.

As published in Biogerontology, Stern and colleagues from the University of Arizona show that starting a moderately-reduced calorie diet with 15% fewer calories than a standard diet at a young age improves metabolism and physical health throughout life. The moderate calorie-restricted diet improves lean muscle mass during midlife, reduces lifelong insulin resistance, and enhances physical strength as measured by grip strength in mice. These findings support the notion that more feasible, moderate calorie-restricted diets confer benefits for healthy aging.

Modest Calorie Restriction Bolsters Lean Muscle Mass Throughout Life

Since lower lean muscle content throughout the body is associated with an increased risk for ailments like type II diabetes, Stern and colleagues examined how a moderate calorie-restricted diet affects lean body mass. The dietary regimen began at four months of age, the equivalent of 26 years old for humans. The research team used an imaging technique called nuclear magnetic resonance to measure lean muscle. The Arizona-based team found that lean mass was higher in 10-, 18-, and 26- and 28-month-old mice on the reduced calorie regimen, equivalent to 40, 56, 72, and 80 years old in humans. These findings provide evidence that a modestly reduced calorie diet significantly improves the lean muscle profile of mice.

Moderate Caloric Restriction Enhances Lifelong Metabolism and Physical Function

Because higher insulin resistance is a risk factor for the age-related metabolic condition type II diabetes, Stern and colleagues measured insulin resistance throughout life. At 10, 18, 26, and 28 months of age, the equivalent of 40, 56, 72, and 80 years in human terms, insulin resistance was almost cut in half with the dietary regimen compared to mice fed a normal diet. These results provide some support that the modestly reduced-calorie diet started at four months of age, the equivalent of 26 human years, improves metabolism. 

Reduced physical function is associated with age-related frailty and an increased probability of mortality. For this reason, Stern and colleagues examined how the modestly reduced caloric dietary regimen affects physical strength by measuring grip strength. Mice in all four age groups, the equivalent of 40, 56, 72, and 80 years old in humans, displayed increased grip strength when given a diet with a 15% calorie reduction. These findings lend further support that by modestly reducing calorie consumption, we can improve our physical function as we age.

“Our findings indicate that a moderate, maintainable level of calorie restriction beginning at early adulthood can limit the decline in metabolic and physical (strength, balance, and coordination) function with aging in mice,” said Stern and colleagues.

Adhering to a calorie-restricted diet without excessive discomfort from hunger and more importantly, malnutrition, is the most ideal way to extend one’s healthspan. Previous studies using non-human primates (rhesus monkeys) show that 10 years of a dietary regimen with a 30% reduced calorie intake reduces body fat, improves insulin sensitivity, and reduces insulin levels circulating in the blood. Moreover, a lifelong 40% reduced-calorie diet has been shown to significantly eliminate liver fat in 18-month-old mice, the equivalent of 62 years old in humans.

The troubling aspect of these studies is that most people don’t have the discipline to adhere to 30% to 40% calorie-reduced diets for extended periods. For this reason, the findings from this study suggesting that a more modest reduction in calorie intake may improve metabolism and physical function offer a glimmer of hope to those who use this dietary strategy.