The reason most diets and weight loss programs work for the short-term but fail miserably, on the long-run, is because they ignore how your body works, at the biochemical level. I'll give you an example.

It is a very common practice for promoters of weight loss cures and "detox" programs to administer a very low calorie diet int he first days of the regimen. The (HCG diet, for example, uses a very low calories diet of about 500 calories per day for the first 21-38 days), to induce some significant weight loss. Most of the other popular weight loss diets available today include a two-week kick-start phase, during which you are likely to lose 10 to 15 pounds. And, to be fair, I realize how encouraging it can be to see this happen. A pound lost is a pound lost, right? Or is it?

A Tale of Glycogen and Water

Spoiler alert: after you read the next few paragraphs, you are likely to become a lot more skeptical of diets that promise rapid, double-digit weight loss. You will also learn something new, unless you are already an expert in biochemistry, like my friend Kyle Craig.

First, you need to know that glucose, a simple carbohydrate, is the preferred fuel used by the brain and most muscles. Second, you need to understand that our bodies are designed with a way of storing several days' worth of glucose in the form of glycogen, which is deposited in muscle tissue and liver when food intake is normal or abundant. When we sleep or fast or eat significantly less food than we need, part (or most, for longer periods of negative caloric balance) of the glycogen is broken down into glucose, to be used as fuel. This is one of the reasons your blood sugar doesn't drop to dangerous levels over night, despite the fact you last meal was 12 or more hours earlier. In people with diabetes, this process is in overdrive, causing elevated fasting blood sugars, despite not eating, like I said, for many hours.

A 200 lbs. adult has about 3 lbs of glycogen stores in his or her muscles and tissues (15g/kg body weight).

The other thing to keep in mind is that glycogen is stored in the body with water, at a ratio of 3-4 grams of water for each gram of glycogen.

A 200 lbs. adult has about 9-12 lbs of water bound to their glycogen deposits.

Let's assume a 200 lbs. adult woman decides to go on the HCG diet. During the initial phase, she would eat only about 500 calories per day, which is more than 1,000 calories less than what her body needs. The result is a situation in which her glycogen deposits are relied upon heavily during the first 2-3 days of her dieting to provide the glucose her body needs, which causes these stores to be depleted.

If we do the math, she can lose a total of 12-15 lbs. in the first few days of following the HCG diet. Pretty impressive, except that none of this weight loss is fat loss. What she actually lost was 3 lbs. of glycogen and 9-12 lbs. of water.

Does It Really Matter?

I guess one could argue that, at the end of the day, it doesn't really matter too much what we actually lose, as long as we lose weight. Perhaps, but we have to remember that as soon as the lady in the example above resumes her usual diet, those glycogen stores will be replenished right away, together with the water, and those pounds lost at the beginning will inevitably come back. For this reason, this initial loss can serve, at best, as a confidence booster, but at worst it can serve to cement a misguided confidence in a short-term solution for weight loss that will lure her back into trying it again in the future. The result is a vicious cycle of on-off dieting, and a physiologically unhealthy yo-yo fluctuation of her weight, with the ultimate result of progressively slowing down of her metabolic rate(studies show a 7-12% reduction, regardless of whether exercise is used to try to conteract it). This will make losing weight increasingly harder, and it is a counter-productive way of doing things. It is similar to getting a $50 bonus for spending $3,000 on a new credit card, without being able or willing to make plans to pay that balance back right away. What you lose in the long-term is a lot more than what you gain in the short.

The other issue I have with very low calorie diets (500 calories/day) is that after they use up your glycogen deposits, you will end up losing more muscle mass, compared to more balanced, low calorie diets (1,000 or more calories/day), as the body will sacrifice some muscle tissue, in addition to fat deposits, to generate glucose.

There are many other reasons you should be cautious about these extreme diets:

high risk of developing gallstones

heart damage, impaired heart function, dangerous arrythmias, heart muscle loss and heart attacks or sudden death

When it comes to weight loss, if it sounds too good to be true, then you can be certain it is.

Ready for the next step? Head over to the fourth commandment of weight loss!

Dr. Gily Ionescu MD, MS.