Functional Foods in fad diets: A review

Background: Fad diets can be defined as any diet making claims that are unrealistic and not supported by evidence-based data. Having been developed since the early 19th century, fad diets promise drastic weight loss and/or other unsubstantiated health claims, often omitting entire food groups. Their popularity with the public makes them an important topic for nutritionists and clinicians, especially in the framework of the obesity epidemic. Additionally, it is conceivable that components of fad diets can indeed facilitate weight loss, even if the diet overall is without merit. The grapefruit diet, the cabbage soup diet, and the human chorionic gonadotropin (hCG) diet are among the most popular fad diets and are reviewed within this study not only in terms of the diet plan itself, but also in terms of possible and known weight loss and health benefits provided by the foods on which the diets are based. Bioflavonoids in grapefruit, including naringin, hesperidin, and bergamottin, may benefit glucose homeostasis. Cabbage contains lutein, zeaxanthin, kaempferol, quercetin, and apigenin, which have anti-inflammatory properties and improve both glucose homeostasis and fat metabolism. The hCG diet is frequently supplemented with non-hCG preparations, which often  contains African mango, which has been shown to enhance weight loss by an unspecified mechanism; astragalus root, which has antioxidant, anti-inflammatory, and peroxisome proliferator-activated receptor-gamma receptor agonistic properties; arginine, which stimulates lipolysis; glutamine, which has been shown to enhance weight loss, perhaps by altering the gut microbiome; carnitine, which appears to facilitate weight loss; B12, which improves insulin resistance; and niacin, which improves the dyslipidemia associated with overweight/obesity. Presently, high quality clinical trials suggest that fad diets reduce weight in the short term due to drastic caloric restriction rather than functional food properties. However, the proof of principle has been demonstrated, and clinical trials of the functional foods utilized in fad diets are much needed.Keywords: functional foods, Fad diet, weight loss, naringin, hesperidin, and bergamottin