K is for Ketogenic Diets

The Atkins Diet, and then the Dukan and others have got dieters into counting carbs rather than calories.

The secret of such diets is said to rest on a process called ketosis. Our usual energy source is glucose, which comes from eating carbohydrates, be it a baked potato or a Mars bar. But if you severely restrict carbohydrates, to 60g or less a day, the body switches to another energy source: stored fat. The process of burning fat means you get a rise in your blood of ketones, acidic chemicals that are released as part of fat metabolism, and account for the ‘pear drop’ breath of ketogenic dieters.

Opponents, however, say low-carb diets make your body acidic, potentially leeching away calcium and minerals, and possibly lead to kidney problems. They often encourage people to eat more saturated fats and therefore could increase the risk of heart disease, even if you are thinner, and restrict or ban vitamin-rich foods such as fruits and some vegetables. Such diets go against current healthy eating advice, which is to base your meals on carbohydrates and low-fat foods.

Proponents of low-carb diets, including some NHS obesity medics, argue that low-carb diets are safe, the medical objections are theoretical and not proven, and not all low-carb diets encourage eating excessive saturated fat. They are an effective way of losing weight and the government is doing dieters a disservice by encouraging the overweight and obese to eat carbohydrates when these may be the problem in the first place. Furthermore, low-carb diets are in line with how our bodies evolved as hunter-gatherers: ketosis is a survival mechanism to see humans through times of food shortage. Ketogenic diets are healthy, they argue, not least by helping you lose weight. One reason for this is that ketones are appetite suppressants, so you feel less hungry and eat less. Perhaps the way such diets work is, at least in part, down to calories after all.