Having been around a while, I have seen celebrity endorsed fad diets come and go. One of the most recent trends is the gluten-free diet. This diet has been presented as a way of losing weight and some have even suggested that it can help with autism. While various celebrities have promoted this diet, health advice from celebrities should be subject to proper critical assessment.
As might be imagined, people have a tendency to confuse celebrity status with expertise. That is, people often believe what a celebrity claims is true because the celebrity is famous. However, while reputation is a factor in assessing expertise, the reputation has to be within the field in which the person is making the claim. So, for example, a person’s fame as an actor has no relevance to her ability to make credible claims about diets. There is also the fact that a person’s expertise depends primarily not on their fame but on such factors as education, experience, and accomplishments within the field. A lack of excessive bias is also an important factor in assessing the claims of an expert. Accepting claims based on unwarranted authority (such as buying into a diet simply because a celebrity endorses it) would be to fall victim to a fallacious argument from authority.
Relying on experts is not, of course, a fallacy. However, one has to be careful to turn to the right experts-that is, people who have the knowledge and experience to be be able to make informed claims and who have the objectivity and lack of bias to be trustworthy. As might be imagined, celebrities who are pushing specific products would tend to be lacking in both areas.
As a specific example, consider the fad of gluten free diets. Like some fad diets, there is some truth behind the fad. In the case of gluten, there is a condition called Celiac Disease. People with this disease need to have a gluten free diet in order to avoid various health problems. While this is a real condition, only about 1% of the US population has Celiac Disease. As such, 99% of the population does not need a gluten free diet.
However, those pushing a gluten free diet claim that it has health benefits for people who do not have this disease. If so, then the diet would be worth considering. However, there seems to be no objective scientific data supporting these claims-thus there would seem to be no reason for people who lack the disease to go on such a diet.
But, one of the main reasons for going on a diet is weight loss and the gluten free diet has been pushed as a means of losing weight. However, the evidence is that the gluten free diet has no special capacity to cause weight loss. See, for example, Wendy Marcason’s “Is the Evidence to Support the Claim that a Gluten-Free Diet Should Be Used for Weight Loss”, page 1786 in in the November 2011 Journal of the American Dietetic Association.
As has long been known, weight loss is primarily a matter of expending more calories that you take in. While gluten products do have calories, gluten calories are simply calories-as are non-gluten calories. In fact, as Marcason points out, some gluten free products have more calories and fat than their gluten containing counterparts. Eating such products in favor of the lower calorie versions will, obviously enough, not promote weight loss.
From the standpoint of thinking well about these matters, there are three main points to take away from this. First, celebrities are not (unless they are also health experts) experts on dieting and health. Second, advice about dieting should be sought from the actual experts-who are generally not celebrities and who tend to give mundane advice like “eat less, eat better and exercise more”. Third, losing weight is a matter of expending more calories than one takes in and there is obviously no fad diet that can change this basic equation. Naturally, a good diet is also more than just a matter of calories-there is also the rather critical matter of nutrients (ironically, there are people who are both obese and malnourished at the same time). But, do not take my word for it-listen to the experts.