There is something enticing and optimistic about a brand new diet. Like buying a cream to eliminate wrinkles or a set of language tapes to finally learn French, we hope that this time THIS diet will work. This new diet will detoxify the liver, decrease the acidity of our stomach, remove those inflammation-causing glutens from our blood stream, burn the fat, increase muscle mass, and eradicate any desire we have for food... permanently. Just the past month, magazines and newspapers have touted the advantages of a 10-day detox diet, an alkaline diet (no foods can be eaten that lower the pH in the stomach) and the life-affirming effects of avoiding any food that is white (cottage cheese, chicken, and yogurt excepted).
Novel ways of eating in the interests of losing weight have been put forth for decades. Liquid diets have come and gone and will come again. Eating certain foods on specific days (does anyone remember the Beverly Hills diet?), fasting, the Atkins fat and protein regimen, diets based on blood type, personality, and presumably on whether one uses a Mac or PC, keep popping up in both respectable and sketchy magazines. Indeed, I am seriously contemplating inventing the Patriotic Diet in time for the 4th of July. This novel diet insists that the dieter eat only red, white, or blue foods on specific days of the week during July. In addition to honoring our flag, the diet could promote weight loss or at least make the dieter dislike red, white and blue foods based upon an aversion through restriction model.
My diet is not real, but alas others with little more great authority and scientific basis are. They are marketed so the dieter believes that they will really work. And for a while, they do.
They work because they are examples of the effect of a placebo on changing behavior. A placebo is defined as an inert, inactive substance or intervention or device without any function. For decades clinicians have found that placebo treatments, e.g., the sugar pill or colored water or sham acupuncture needle, really do work to reduce pain, depression, and a large variety of other ills that seem impervious to medical treatment.  The explanation is that if one believes something is going to work, in many cases, it does. So if a new diet comes along that claims to detoxify my intestinal tract, rejuvenate my liver and make me energetic and happy, I may reap these benefits because I truly expect that these things will happen.
Another reason is a logistical one. Diet plans that target certain foods for consumption or avoidance must by necessity eliminate large numbers of foods that are fattening. Do away with bread, and presto! One therefore also eliminates butter, cream cheese, peanut butter, mayonnaise, cheese spread, and Nutella. Tell people that dairy products will do dreadful things to their gut and they right away stop eating not only fat-free yogurt and skim milk, but ice cream as well. Having a newly-discovered gluten sensitivity used to be a reliable way of losing weight because so few foods could be eaten. Now, alas, so many manufacturers are making gluten-free foods which resemble the old foods we used to eat problem-free, that it is hard to eliminate much from our diet.
Alas, there is no placebo for smaller portions, lower-calorie foods, substitution of vegetables and fruits for chips and cookies, and none for exercise. New diets become old very quickly as the weight returns and the diet plan is shoved under a stack of others that are no longer interesting.
The weight-loss plans that work are boring, predictable, slow acting, and do not make for interesting conversation. Very few people who exercise consistently rarely consider their workouts sufficiently unique to chat about them with others. (Golfers are an exception.) Who wants to know how many minutes your neighbor spent on an exercycle or doing a yoga pose? People who always eat salads, fish, low-fat dairy and steamed rice rarely mention these foods as the newest diet fad in the tabloids. Who wants to know how many servings of vegetables you ate this week or cups of cottage cheese you managed to swallow? Alas, a boring, slow weight loss, sensible diet will not make celebrity headlines or you, the follower, the center of attention at a party.
A new diet-a-day will not make the weight go away. What will make it go away is finding and following an eating and exercise plan that works for you, day after day, year after year. Eventually having a fit, thinner, healthy body will no longer be a novelty. It will simply be a way of life.