Aging can be considered rust of the body as a result of oxidative stress. The act of fueling yourself and digestion contributes to oxidative stress. Can calorie restriction (CR) have an effect on longevity? The largest clinical trial to date on this topic found that during the 2 year course of the trial that healthy, non-obese subjects experienced both metabolic slowing and a reduction in oxidative stress associated with calorie restrictions.
One of the most consistent benefits discovered from CR is a rapid reduction in high blood pressure. Studies have shown that BP can be normalized in as little as two weeks, eliminating the need for high BP medicine. In some cases, this lowered the BP too much and resulted in orthostatic hypotension or even fainting.
Another frequent finding of CR is that while you lose weight, your body composition is not what is desired. During a period of CR your body tends to cannibalize lean tissue rather than fat. This is similar to previous findings we discussed on a keto diet where you actually lose weight, but the lean mass is what is lost the most. It is often suggested that an increase in protein intake could combat this lean mass loss. However this isn’t borne out in clinical trials. Studies that has CR participants engage in a normal protein diet vs a high protein diet found no meaningful difference in lean body mass loss. Worse still, high protein diets combined with CR results in profoundly negative metabolic effects. For example, weight loss associated with CR can greatly improve insulin sensitivity, but the same WL on a HP CR diet is no better than when the subjects started.
How to prevent LBM loss during CR? Exercise. Specifically, resistance training. Meta-analyses have shown that strength training just 3x a week prevents 93% of the LBM loss induced by CR. The same regiment of RT also halted any associated bone density loss associated with CR.
In general, CR has been shown to improve:
Blood Pressure
Cholesterol
Mood
Libido
Sleep
Researchers with the Journal of the American Medical Association stated, “The findings of this well-designed study suggest that intake of excess calories is not only a burden to our physical homeostasis but also on our psychological well-being.”
How to Implement Calorie Restriction
You are presented with many choices to achieve calorie restriction: Simply reducing calories at meal time consistently, total fasting for a period of time, intermittent fasting, or calorie restriction on a periodic basis, say, every other day. How to choose?
Fasting:
Any fast over 24 hours should be truly only be done with medical supervision, breaking the fast can be particularly dangerous. In WWII, it was observed that as many as 20% of liberated, starved Japanese POWs died when they resumed eating.
Cons
By its very nature, this is, at best, a yo-yo strategy, and historically these types of diets don’t work in the long run.
Vitamin and mineral deficiency can develop very quickly, two to three weeks
Some vitamin and mineral deficiencies, once manifested, can be irreversible
Loss of water and dehydration can damage kidneys
Electrolyte imbalances
Destruction of heart muscle has been documented in longer periods of fasting
Refeeding Syndrome: Multi-organ system failure can occur when resuming a normal diet too quickly
There are numerous contraindications for fasting: eating disorders, pregnancy, hyperthyroidism, liver or kidney insufficiency, and tendencies for hypoglycemia.
Weight loss on total fasting is disproportionately lean mass, not body fat (see below)
Pros
Psychological benefit of proof that weight loss is possible
Can act as a jump start to changing long term eating habits and lifestyle
In an NIH funded study, a series of obese subjects were placed in three phases of diets (each participant went through each phase). Phase 1 was two weeks a calorie restricted diet (800 calories a day, but not a total fast (starvation) diet. The average daily body fat loss was about one pound and lean tissue was just a few ounces. Next, the subjects were then switched to two weeks of a zero calorie diet. The loss amounts switched: just a few ounces of body fat, but about a pound of lean mass per day. Finally, the subjects were put back on the low, 800 calorie a day diet for the final week. The same pattern observed in phase 1 resumed. The researchers concluded that the subjects would have lost more body fat overall had they not fasted, but instead stayed with a steady low calorie diet.
In general, the medical community has abandoned prolonged fasts not only for the risks outlined above, but also because of the questionable results that can be achieved. When compared to a low calorie, non-fasting diet, subjects generally lose less body fat fasting.