THE RECENT UPSURGE in the popularity of intermittent fasting as a tool for weight loss motivated me to examine this concept in detail. What is meant by intermittent fasting? Intermittent fasting (IF) is a pattern of eating based on timing. It does not prescribe what you eat, rather it tells you when to eat. The impact of any conventional weight loss programme based on daily calorie restriction is limited by the fact that our bodies adapt to it over a few months, resulting in prevention of further weight loss. Intermittent fasting attempts to circumvent this adaptation by cycling between a very low-calorie intake for a brief time followed by normal eating, so that the body physiology is unable to adapt to a low-calorie intake. The concept of IF is ancient as is evidenced in Greek texts and religions like Buddhism and Jainism.
There are several types of IF:
1. Eat stop Eat and 5:2 diet—The eat stop eat diet involves 24-hour fasting on two non-consecutive days a week. The diet aims at creating an overall calorie deficit. On fasting days, only non-calorie beverages are allowed. On the 5 ‘eating’ days, normal food is consumed. However, absolute fasting for 2 days every week can be demanding, and can make one feel hungry and irritable. The tendency to overindulge on eating days can negate the weight loss benefits. The 5:2 diet is based on a somewhat similar concept, with 500-600 calories being allowed on the fasting days, instead of absolute abstention.
2. Warrior diet—This involves 4 hours of eating and 20 hours of fasting on a daily basis. All the intake is concentrated over just four hours in the night. It mimics eating patterns of ancient warriors of Sparta and Rome, who ate little during the day and feasted during the night. During the 20-hour fasting period one is allowed fluids, and small amounts of fruits, ‘green’ vegetables, nuts, eggs and dairy such as yogurt and cottage cheese. Exercise is always integrated into the plan—but many find it taxing during the fasting period. It can also be a challenge to pack all nutrients required by the body in 4 hours of eating, and stomach discomfort and bloating are common complaints.
3. Leangains—It is the most popular diet because it is the least demanding and causes least interference in one’s social life. It was originally designed for weightlifters. The daily periods of fasting and feeding are 16 and 8 hours, respectively. Typically, the fasting period is through the night and up to noon the next day. If you are a late-night worker, you can start your fast even after midnight and break it between 4-6 pm. However, the timings should remain constant each day to let your body settle into a rhythm. Only non-calorie beverages are allowed during the fasting period. Ideally it is accompanied by a detailed workout and weightlifting plan.
4. Fasting mimicking diet—It is a fascinating concept which involves consuming a plant-based diet for five consecutive days every month. The diet is low in carbs and protein but high in healthy fat like olives and flax. The first day of the diet provides about 1,000 calories, and the remaining days only about 700. The other 25 days of the month the person is free to eat what he likes.
The overall benefits that all these diets claim are greater weight loss, and more effective lowering of blood sugar and cholesterol levels as compared to conventional diets. Superiority of one IF protocol over the other remains unclear. Animal experiments suggest benefits like reduced insulin resistance and improved pancreatic insulin secretion, reduced cognitive decline, and potentially a decreased risk of cancer via a reduction in growth factors. One of the most remarkable effects is on autophagy, a process by which denatured proteins are removed from cells, or changes in gene expression, both of which may be responsible for increased lifespan.
Evidence that IF is clearly superior to conventional calorie restriction for weight loss in humans is still lacking. A systematic review of diets that compared IF with continuous calorie restriction found that both diets induced significant weight loss (3-4 kg over 10-12 weeks). What was surprising was that dropout rates were also similar between both groups. Adherence to IF for prolonged periods is a challenge. Possibly the major reason for benefit from IF could simply be the reduction in calorie intake. I recommend it only if conventional continuous diet regimes fail for individuals with obesity, pre-diabetes and early diabetes. Those on complicated diabetes regimens are advised to avoid IF. Regardless of what diet you follow, make sure with your nutritionist that it does not lack essential nutrients.