Carbohydrates are essentially just long chains of glucose molecules strung together. Glucose is a sugar, which requires insulin in order to be taken up by cells. When carbohydrates are metabolized (digested), the effect on the body is virtually the same as if one had eaten the same amount of sugar. The type of carbohydrate can make somewhat of a difference; fast-digesting carbohydrates, like those in white bread, pasta, or white potatoes, can cause a large enough glucose spike that is almost indistinguishable from eating the same amount of sugar; slower digesting carbs, such as in vegetables, not so much.
Glucose restriction extends lifespan in C. elegans
It’s been found that in the model organism C. elegans (a tiny worm frequently used in aging studies), restricting glucose from their diet results in longer life: Glucose Restriction Extends Caenorhabditis elegans Life Span by Inducing Mitochondrial Respiration and Increasing Oxidative Stress.
The fact that glucose restriction induces oxidative stress appears to be key here, since that makes glucose restriction a form of hormesis, which the authors dub “mitohormesis”, since it acts upon the mitochondria. As a form of hormesis, glucose restriction induces antioxidant enzymes such as catalase, and causes an upregulation of cellular stress defense mechanisms.
Antioxidants abolish lifespan extension
Importantly, treatment of these worms with antioxidants abolished life extension, which shows that the increased oxidative stress is necessary to for increased longevity. Glucose restriction also caused an increase in fat burning. Also importantly, disruption of the worm equivalent of AMPK abolished lifespan extension by glucose restriction, showing that activation of AMPK is necessary. As we recently saw, activation of AMPK alone, by whatever means, be they chemical compounds, drugs, exercise, or fasting, increases lifespan, since AMPK controls the aging process.
Addition of glucose shortens lifespan
Next, we see that the addition of glucose to the food of C. elegans does just what we would expect: it shortens lifespan. The authors refer to glucose in this regard as “a potent lifespan-shortening agent”.
Low-carb diets, antioxidants, and longer life
A co-author of this second study was Cynthia Kenyon, one of the most renowned aging researchers, who now works for Google in their start-up anti-aging company, Calico. When Kenyon made this discovery about glucose and lifespan, she gave up refined carbohydrates, and eats a diet that looks very much like paleo. I think the rest of us can take a lesson from this.
The fact that antioxidants abolished the effect of glucose restriction on lifespan means, in my opinion, that one should be careful about supplementing with them. On an intermittent fast, for instance, one shouldn’t take them, and if extra vitamin C is desired (which I take myself), it should be in rather small amounts, say 500 mg, and taken in the fed state and away from workouts.
Probably the biggest caveat here is that these studies were done in nematodes (worms), and to my knowledge it has not been repeated in mammals. However, glucose does increase insulin/IGF-1 signaling, and it is known that decreased insulin/IGF-1 signaling increases lifespan, so to me that’s a fairly compelling reason to think that these results are applicable to mammals.