The Mechanisms of Calorie Restriction

Initially, the descriptions of life extension with calorie restriction seem radical, but studies have confirmed the relationship many times over in multiple species.

Essentially, slower development and lower growth also resulted in longer life spans.

Why? There are many potential mechanisms.

Low body fat is perhaps the most obvious effect of chronic calorie restriction in animals, but low visceral fat is of particular importance.

High visceral fat, which is stored inside the abdomen and around major organs, poses a significant health risk to humans and is closely associated with decreased insulin sensitivity, obesity, type 2 diabetes, and atherosclerosis.

Mice genetically engineered to have very low body fat live longer.

FIRKO (Fat Insulin Receptor Knock Out) mice have disrupted insulin receptors.

Because insulin normally tells the body to gain fat, these genetically engineered mice cannot become obese, and they also live longer than unaltered mice.

Both FIRKO and calorie-restricted mice have greatly reduced body fat, which suggests that less body fat might be the common denominator that extends lifespan.

But that’s not the whole story because being underweight or having lower-than-normal levels of fat also is associated with health risks.

However, there’s a large confounding factor here.

Underweight people may have hidden illnesses, such as cancer, that cause the underweight condition, so it is unknown if deliberately lowering body fat below normal is healthy or harmful.

Chronic calorie restriction decreases the metabolic rate.

If you eat fewer calories, your body responds by burning fewer calories.

At first, this may not seem beneficial, but a lower metabolic rate correlates with less oxidative damage to DNA and therefore might affect aging.

Different animals have widely varying metabolic rates.

In general, the higher the metabolic rate, the shorter the animal lives, possibly due to freer radical or oxidative damage.

If you are constantly reviving your car’s engine, it will go faster but burn out sooner.

In humans, lower levels of free triiodothyronine (T3), a hormone important for metabolic rate, are associated with longer life.

Although calorie restriction can lower the overall metabolic rate, energy expenditure per gram of body weight may be higher.

Some reports have found healthy centenarians to have both greater muscle mass and a higher metabolic rate, both of which are correlated.