Does fasting work?

More and more scientists are looking into fasting and intermittent fasting (IF) as an aid to control obesity and its potential health benefits. However research is still in its infancy and there are as yet no hard facts as to the long term benefits to fasting in humans.

After reading much of the science on this topic and experimenting myself with intermittent fasting I am surprised at the ease that I have adapted to this kind of eating. Whilst the diet books suggest either the 5:2 plan, where you cut your calorie intake to 500/600 calories  (women/men intake levels) for two days of the week and eat whatever you want on the remaining five days. Or the alternate day fasting where you reduce the times you can eat to between 11am and 7pm, every other day. I found that listening to my own body provided me with natural times where I wasn't hungry and so didn't eat. From an early age we have been taught to eat at set times of the day and so most of us are habitual eaters. Combine this trend with the availability of easily accessible, highly refined foods, we end up with an obesity problem.

Look back to our ancestors or our primate cousins and we find that they are opportunistic eaters. They spend a lot of time being physically active finding their food, and they don't eat processed foods and as a result don't get fat. We have evolved to eat when food is available and to efficiently store excess calories for lean times. I have found that by ignoring the clock when it comes to eating and listening to my body, fasting comes naturally. Frequently I wake and don't feel hungry till mid morning or sometimes mid afternoon, at that point I eat a healthy balanced meal.

The hard part is learning to distinguish actual hunger from the cravings I get for sweet and fatty foods. The cravings are difficult and in my opinion akin to the overwhelming need alcoholics express for another drink. They are however beatable and every day it gets a little easier to ignore the sugar beast.

The problem I see with the 5:2 or IF plans is that people assume that on the feast days they can do just that, feast, but they feast on all the foods that our body finds easiest to store as fat. Put simply our bodies burn food as fuel, you need some fuel for your body to tick over and some to provide energy for your daily activities, plus essential nutrients and vitamins to keep your body healthy. If you put less calories in to your body, your body is programmed to release the fuel it stored as fat to keep you alive.

The reason fasting seems to work well and has additional health benefits beyond weight loss and the factors associated with weight loss, is that during fast periods reduced levels of the insulin like growth hormone somatomedin C (IGF-1) causes our bodies to switch from growth mode to repair mode. This switch in cell function has shown in various animal studies that the effects of aging and some forms of cancer are reduced.

We are however in the early days of fasting science, so don't believe the hype from the people selling you this new miracle diet. Getting healthy is going to involve work and a lot of common sense. Fasting as part of a balanced diet can work for some people but not everyone. Whilst a 900 calorie meal of burger and fries is not off the menu in any balanced diet, common sense should tell you there might be a slightly healthier compromise and that this type of food should be a monthly occurrence, not daily.

The Science:
V. D. Longo - Evidence for Programmed Aging
American Journal of Clinical Nutrition July 2007: 86(1); 7-13
Journal of Clinical Endocrinology and Metabolism 1991:74(4); 757-765 (PDF)