I've been pretty sceptical of the alternative health and diet industry for some time, and the turning point was back in about 2000 when someone introduced me to something called the "Mayo Clinic Diet", an ultra low calorie that was supposedly given to cardiac patients to lose weight quickly before surgery and based mostly on pork chops, boiled eggs and grapefruit. I tried it for a couple of days but something didn't seem quite right. For a start you only ate about 500 calories a day, and second red meat and eggs are pretty high in cholesterol and saturated fat which a cardiac ward certainly wouldn't recommend. I did a quick Google and the first link I found was from the real Mayo Clinic which said "this is nothing to do with us and could be potentially dangerous". After reading that I immediately stopped it and went out to buy a nice pie.

The basics of nutrition are pretty straight forward: food contains a mix of fat (including fatty acids and related compounds such as sterols in plants or cholesterol in meats), carbs (as starch or sugars), protein, dietary fibre and micronutrients such as vitamins (certain types are called antioxidants, although the body can produce some antioxidants by itself) and minerals. The body processes these in different ways. Fats become adipose cells, carbs are used for energy, protein is used to build muscles, fibre is indigestible, and micronutrients have other purposes such as calcium being used for bones and iodine being concentrated in the thyroid gland. All are essential, but the important bit is the amount you eat. Cutting out carbs can make you feel weak and dizzy because of low blood sugar. Lack of fibre can cause constipation. Most western diets have plenty of fat and protein. However high protein foods tend to be things like meat and nuts which are also generally pretty high in fat. Meanwhile the respiration process uses up the body's reserves of energy. The more active you are, the more energy you use. Carbs go first, then adipose fat, then muscle mass. In order to lose weight you need calories expended to be greater than calories in, but not so low that the body goes into starvation mode.

This is GCSE level human biology and understanding the digestion/respiration process from a scientific point of view is a good antidote to the many quacks and charlatans there are. One therapy I've heard of involves pouring coffee up your backside (I just hope it's not fresh off the boil!). Food supplement pills are also very commonly promoted even though they either contain far less than standard foods or contain more than the body can handle and end up passing through and being flushed down the loo. This is why one of the side effects of vitamin B tablets is bright yellow urine. There's no such thing as "catalyst" foods, and the idea of "negative calories" (foods that apparently take more calories to digest than they provide) came from a single study of overweight women over 40 which found that eating plenty of fresh fruit and veg led to weight loss.

Fad or proprietary diets tend to have some kind of gimmick to encourage you to follow them. Atkins is a low calorie one that excludes carbs. Most "detox" diets are ultra low calorie ones that exclude cooked foods. However some foods (such as potatoes or certain types of bean) contain toxic compounds that are broken down by cooking, and it would be a very brave person that tried eating raw chicken. "Detoxing" is another nonsense: the body processes most things within about 24 hours, and genuine poisoning usually needs some treatment other than not eating "processed" food. There's an interesting article about detox here and the rest of the Sense About Science site is worth a read as well, especially "I've got nothing to lose by trying it".

The science is the easy bit. What's tricky about weight loss is keeping the intake under control, which is a lot more psychological. Some people like the support of a weight loss group such as Weight Watchers or Slimmers World. Others like sessions with motivational speakers or hypnotherapists. Another option is doing it with friends or by setting some target. This is where the diet industry comes in. I know a certain mindset might find it difficult to understand that I've lost nearly 50 kilos simply by eating standard food that you can get from a supermarket, but it's fair to say I've got very good self discipline. There's no "right" answer to what might keep you motivated, you've just got to try a few things and find one that works.