As relentless as wind-chill is the arrival of diet books in January. It is the month that book and magazine publishers cash in on the holiday season pig-out--and guilt about enjoying yourself Thanksgiving to New Year's.

And of course all the diets claim to "take it off and keep it off."

But then, so did the diets you tried last year. And the ones the year before, and the year before that . . .

As usual, the current crop of diets ranges mostly from the frankly dangerous to the tried, tested and found-wanting "balanced diet." Nevertheless, there is one standout that may be at the leading edge of a breakthrough, and possibly the most interesting diet-related development in some time: the serotinin connection.

Serotonin is a neurotransmitter, one of those electro-chemical brain messengers that help the brain run the complex functions of the human body. Neurotransmitters can affect things like mood and behavior, appetites (of all sorts), anxiety, alertness, even sleep, depending on readings from the body's seemingly limitless feedback mechanisms.

Serotonin generally has a calming effect on the system and a lack of it has been shown to interfere with sleep. Now, however, research at the Massachusetts Institute of Technology is finding that a lack of serotonin may also trigger cravings for carbohydrates, that indeed, it plays a role in the system that "keeps the bear from eating nothing but honey."

The work stems in part from research done by MIT neuro-endocrinologist Richard Wurtman and his cell biologist-nutritionist wife Judith J. Wurtman. Among other things, their findings suggest that a lot more weight problems are chemical then psychological. Judith Wurtman has written The Carbohydrate Craver's Handbook ($12.95, Houghton Mifflin). She spells out the research--on people as well as rats; offers a three-day self-test for readers to rate themselves as carbohydrate cravers, and makes some interesting suggestions for keeping brain chemicals happy and your urge for something sweet or starchy at a minimum.

As Judith Wurtman writes of an experiment she did with rats, "We assumed that if rats needed to eat carbohydrates it wouldn't be because their mothers had given them cookies when they fell out of their cages, or ice cream when their tails were pinched . . ."

Wurtman's rats were given a high-carbohydrate snack (devised from a candy recipe in the Joy of Cooking) or peanut butter (rats love peanut butter, in case you didn't know). The rats who got the peanut-butter snack chose carbohydrate-heavy foods to eat at their regular meals; the ones who ate the candy went on to eat other foods, their carbohydrate craving now satiated.

Wurtman's diet is based on a system of calculated snacking on foods high in carbohydrates: even, for some folks, M&Ms. Later, at a proper meal, the consumption of protein helps abate the craving.

This is because of the serotonin connection which works like this: An amino acid called tryptophan is found in proteins like fish and chicken. The brain uses tryptophan to synthesize serotonin which, in turn, shuts off the craving for carbohydrates. Tryptophan, however, gets to the brain on the same "transport system"--a carrier-molecule--as five other amino acids that are found in proteins. Tryptophan, the rarest, is easily crowded out by the other, more numerous amino acids.

The brain thinks the body needs more carbohydrates and sets the craving in motion. Carbohydrates stimulate the release of insulin which, among other things, disperses the amino acids competing with tryptophan, giving it a free ride, as it were, direct to the brain. Result: The brain makes more serotonin and your body stops craving carbohydrates.

When you eat a carbohydrate snack at timed intervals during the day and follow it later with a meal including fish or chicken, for example, the insulin secreted by the earlier snack will, in effect, pave the way for the tryptophan to get to the brain.

More recent studies, about to be published, on 188 men and women working at an army base outside Boston pretty much confirm that as far as choosing foods, people aren't so different from rats. The people who ate a high-carbohydrate lunch (sherbet) also felt happier and calmer during the afternoon than their colleagues who'd eaten turkey.

Wurtman, a veteran diet counselor, is not about to dismiss all psychological factors in the fat fight. But she does believe that the deprivation of carbohydrates leads to a deficiency of serotonin that leads to not only a craving for carbohydrate but that feeling of depression, misery, irritability and hostility that every dieter in the world experiences. Carbohydrate deprivation over a longer period of time, the studies are showing, also leads to overconsumption later--almost guaranteeing the regaining of lost weight and then some.

The diet she offers, relatively low in protein and high in complex carbohydrates, is still a matter of calorie counting. "It may not be any more effective than anyone else's in getting you to lose weight, because it's still calories-in, weight-on, but what I've done is remove one of the 3,000 reasons why people gain weight back again so quickly--because of rebound carbohydrate eating.

"I can't stop people overeating because they can't stand their mothers-in-law," she says, "but I can make people know that they may also be overeating because they are carbohydrate deprived. On this diet they'll know that at least that is not the reason."

(Although the Wurtman diet is not too different from those that tend to help diabetics and hypoglycemics, no one with even traces of those disorders should go on any diet ever without the explicit approval of a physician, preferably a specialist. People who have any problems with insulin secretion--whether too much or too little--need to be under a physician's care at all times and, especially, should not alter their diets on their own.)