There are several reasons for this caution.

Recognize that the ability to store calories as fat is pro survival, when the food supply various a lot throughout a year. With steady food supplies, this is anti survival. Eat more calories than you need, of whatever type, and you will put on fat. Even excess protein consumption is stored as fat. Note that high meat diets are high in saturated fat as well as protein.

Most people who try to lose weight do not make permanent changes to life style. They can lose a few pounds in the short term, but not keep them off.

Many fast diet schemes are tricks, some even dangerous. Especially bad are those plans which emphasize weight loss, but ignore what component of weight is lost.

WATER LOSS: many plans show quick results because they cause the body to drop water. The medical term for such pills is diuretics. Weight-wrap clothing makes one hot, and sweat. The same is achieved with steam rooms, saunas, and the like. Any professional athlete knows that a typical workout can cause the loss of 1 to 10 pounds of water, or more, which must be replaced to prevent heat stroke, even death.

MUSCLE LOSS: Many plans concentrate on reducing the total calories consumed, which is great if done wisely. The dangerous plans are those that starve the body so that muscle, as well as fat, is lost. As most dieters return to pre diet food practices, the lost muscle is usually replaced with fatty tissues. Muscle mass consumes calories even when the body is at rest. Reducing muscle mass merely to lose weight means that body is less balanced for controlling weight.

LOSS OF INJESTED FOOD: bowel stimulants are okay if needed for constipation, or to aid regularity, but NOT for weightloss. If you aren't eating much raw fruits and vegetables, moderate doses of dietary fiber supplements are okay.

FAT OR STARCH BLOCKERS: Two criteria must be met; they must work, and be safe to the metabolism. None are known to exist. I wrote elsewhere about chitosan, a "fat magnet" that does not work.

APPETITE KILLERS: They exist, but many have been removed from the marketplace. Narcotics are one such drug group.

FEN-FEN or FEN-PHEN, fenfluramine and dexfenfluramine, an anorexic drug, was banned by the FDA in 1997, mainly due to heart valve damage.

An alternative is to hold something nauseating under nose or tongue.

FAT BURNER STIMULANTS: "Fat burners" are a fictitious part of the body. Pills to turn them up have nothing to work on.

METABOLISM ACCELERATORS: Amphetamines rev up the body, and formerly were in wide use by dieters and by students who were cramming for tests, as well as speed freaks. Tolerance requires increasing doses. High doses cause sleeplessness, nervousness and euphoria, and can cause death. Usage can be followed by intense mental depression and fatigue. DON'T!

Late 2003, a class of weight loss pills was taken off the market, due to deaths of athletes and dieters; Ephedra, also called Ma huang, and synthesized ephedrine. Ephedrine alkaloids are amphetamine-like compounds, used in some prescription medications, and found in some herbal teas. The side effects include increase of blood pressure and pulse rate, nerve damage, muscle injury, psychosis, stroke, impaired memory, nervousness, tremors, seizures, heart attacks, strokes. Who needs it?

READ THE LABELS. Many weight loss products contain a lot of sugar, fructose, maltodextrin, thus sugar, sugar, modified corn starch. These are lousy choices for good nutrition, and can bounce blood sugar levels dangerously high, after which they can crash to dangerously low (hypoglycemia). Ingesting too much refined sugar can induce diabetes.

Thus, many "nutritional diet products" are nutritional only if compared to high fat and high salt foods.

FAT RESTRICTION: This should be a permanent part of a healthful food plan for anyone who is not very active physically. Prior to modern mechanization, everyone but the pampered ruling classes used a lot of calories all the time. This is why so many traditional / ethnic foods are high in fat, such as bacon and sausage, pastries, fried foods. What was good for great grand parents can be bad for us.

Here's a cruel truth. A little bit of fat is far more effective than high protein or sugar foods at satisfying hunger. The trick is to avoid saturated fats and trans fats (hydrogenated oils).

Smart dieters can get unsaturated fats from plant foods, such as nuts and seeds. Outdoors enthusiasts are mostly familiar with "trail foods", such as "GORP" = Good Old Raisins and Peanuts. I find that almonds and raisins chewed together are very sweet and hunger killing, so not a risk to weight control.

YOUR BEST DEFENSE against fraud of any kind is self education. Don't be afraid to question what any source says, but consult several sources that have no mission to sell you anything. Government publications and Mayo Clinic advice are good examples which can be reached on the internet.