Philip J. Goscienski, M.D.
Missing a meal or two has no adverse consequences to our health and even going without food for a couple of days, provided that we keep up with our need for water and electrolytes, doesn't cause any significant problems in healthy persons. But what about prolonged fasting or a drastic reduction in calories, as some weight loss programs advocate? When does a low-calorie diet become more risky than simply being overweight or even obese?
Like so many questions in the realm of biology, "It depends." Our Stone Age ancestors rarely or never experienced true famines because they didn't rely on just a few kinds of food. However, over the course of thousands of generations there were undoubtedly times when food was scarce. A migration, severe drought or warfare could mean days or weeks of inadequate food intake. It's likely that such pressures selected out individuals that could tolerate such deprivation and survive in order to reproduce.
Fasting for short periods is not harmful; it probably has some health benefits. Starvation, which is what we do when we deliberately and severely restrict calorie intake, may have significant adverse effects, even if it helps us to melt away lots of excess fat.
When we starve ourselves — arbitrarily define that as eating fewer than 1,000 calories a day — few pounds consist of water and glycogen. (Glycogen is the equivalent of plant starch that animals store mainly in the liver and muscles.) You might think that with continued calorie deprivation fat would provide needed energy but that's not all that happens. The body also breaks down protein to provide glucose, one of only two chemicals that cells use to maintain energy and keep all systems working. That's a bit of a simplification but it results in the loss of lean body mass, largely from muscle but that includes every organ. No wonder that marked weakness and fuzzy thinking are early signs of starvation or dramatic dieting.
Starvation, whether deliberate or not, leads to constipation, tooth loss, dementia and osteoporosis, all of which are among the complications of bariatric surgery. Weight loss of more than two pounds per week is a risk factor for inflammation of the gallbladder.
Gradual weight loss carries minimal risk as long as the diet is fortified with vitamins and minerals. Adequate protein and fiber intake with moderate physical activity will prevent the loss of lean body mass.
Philip J. Goscienski, M.D. is the author of Health Secrets of the Stone Age, Better Life Publishers 2005. Contact him at firstname.lastname@example.org.