recommendation of mainstream nutritionists, who advise multiple servings of grains per day.
Metabolic Typing is seen as essential, which provides adjustments of the diet depending on each person's metabolic needs. Metabolic Typing is based on the assumption that each person has a unique way in which food is metabolized in the body, making it impossible to find one diet which works for all people. Three metabolic types are distinguished as Carb, Protein or Mixed Type, depending on the ratio of carbohydrates, proteins and fats each type of person is supposed to require in his daily diet. The diet is then adjusted to those metabolic types. This part of Mercola's diet appears to be identical to the Metabolic Typing Diet by William L. Wolcott.
Criticism, Debate, Discussion
While the elimination of refined sugars can be seen as a positive step for one who relies solely upon such products to the point of nutritional deficiency (easily fixed by a multivitamin supplement), for one who receives plenty of nutrition, sugar is a source of simple carbohydrates that many may wish to use as an energy burst for intellectual or physical activity.
There is still much to benefit though, as it's likely that we do not use most of this, and should lower (not eliminate) the levels of sugars to a level where we will fully utilize them. Any in excess of that would just be stored as fat, eating fats is better for gaining fat if that is desired since it is a more efficient conversion. The issue of insulin spiking is also a good one. Generally, you don't need to eliminate sugars to manage insulin levels though. Small amounts of high GI foods can be consumed without vastly increasing insulin secretion, just as large amounts of low-to-mid GI foods can still spike them higher. Food is too generalized in this regard.
The elimination of grains is a far more serious matter. Grains offer a unique blend of nutrients that, while possibly obtainable from vegetables, may be on an unrealistic level that, unmonitored, may lead to deficiencies. Thiamin and Fibre, for example, could be deficient be eliminating grain. Grain is also a very cheap source of energy, and if someone switches off of it unneedingly they may be throwing their money down the drain by neglecting it. Grain can be very high in nutrients (especially with the ever-growing popularity of whole grain products) and is recommended by the IDA. While some claim the Dietetic associations have bias (funding from grain product manufacturers for example), this is something to be taken up separately.
However, since surveys show that most people with a sensitivity to gluten go undiagnosed, this is maybe the reason why some people find they benefit from cutting out barley, oats, rye, wheat and any processed food products that may contain gluten from these grains. They may indeed have atypical celiac disease and should see their doctor.