Although many theories have been investigated, the cause of ADHD remains a mystery. None of the results of the experiments have led to a clear and compelling outcome. A nutritional deficiency of some sort remains high on the list of candidate causes (Dietary Theories for ADHD) . Potential deficiencies in several different vitamins and rare metals, such as zinc, magnesium, iron, and vitamin B6 have been posited, but in controlled studies, supplements have failed to show statistically significant improvements. The fact that ADHD appears to be especially prevalent in America suggests that it has something to do with differences between the American diet and the diet of other countries. To me, the most obvious difference is America's obsession with low fat diet. Today it is practically impossible to find full-fat yogurt at an American grocery store, and non-fat or low-fat products crowd out the full-fat versions of the same things on grocery shelves. Marketing ploys are proud to boast that a given product contains little, or, better yet, no, fat.
The nutritional theory for ADHD that has gained the most traction is that it may be caused by a deficiency or imbalance in essential fatty acids. These are omega-3 and omega-6 fats, which are widely available in meats, fish, and eggs. Humans are unable to manufacture these fats naturally from other dietary sources. While omega-6 fats are also found in vegetable oil, omega-3 fats are only abundant in animal fat, especially cold-water fish. Experiments that provide ADHD children with an omega-3 supplement have shown modest but encouraging results. However, I'm not proposing simply adding an omega-3 pill alongside the Ritalin tablet. I'm proposing that the cheerios and skim milk for breakfast be replaced with bacon and eggs; that the diet coke for lunch be replaced with whole milk, and the lean turkey breast in the sandwich be replaced with dark tuna, peanut butter, or liverwurst (a healthy choice that has all but disappeared from America's grocery shelves).
Another theory suggests that ADHD may be due to too much dietary refined sugar . This theory also makes sense because the near absence of fat, coupled with an overabundance of high glycemic index foods, leads to a wildly unstable food supply in the blood. Glucose levels in the blood skyrocket immediately after a meal, and this triggers a sharp increase in insulin supply, rushed out by the pancreas to process the glucose. However, as long as the insulin concentration in the blood is high, fats that are stored in fat cells remain inaccessible and are not released into the blood. Many of the body's cells can utilize either glucose or fats as fuel. However, the brain can not utilize fats for fuel, but, critically, needs fat as raw material for construction of its network of nerve fibers. This is especially true for a growing child with a maturing brain. The brain needs a simultaneous presence of adequate glucose and adequate fat, something that is very hard to achieve when fats are unavailable from food sources, and high glycemic index foods are abundant.
Previous experiments conducted to test whether too much sugar causes ADHD involve substituting aspartame (a zero-calorie sweetener) for sugar . I am not surprised that these experiments have failed, because aspartame is arguably even more damaging than sugar: the sweet taste on the tongue triggers the release of insulin, but there is no sugar for the insulin to break down. Hence the insulin lingers longer in the blood and fat release from available stores is further suppressed.
There is a strong genetic component to ADHD, i.e., it tends to run in families . But this does not mean that the cause is genetic. Instead, genetic factors predispose individuals to develop alternative strategies for coping with nutritional deficiencies, that lead to different, but perhaps equally damaging, health issues. I would argue that, in the case of ADHD, genetics determine how the body manages homeostasis in the face of excess carbohydrates along with dietary deficiencies in essential fatty acids. (With respect to nutrition, homeostasis refers to the maintenance of a stable supply of glucose and fatty acids in the blood under varying conditions of food supply.) Studies to determine which genes are involved in ADHD have turned up hundreds of genes that play a role, but each gene has only a very small influence, so the relationship to genetics is extremely complex.