5 days is way too short a sample. Maybe you're not affected by wheat in which case good for you, but a good chunk of the population is. The tiredness creeps in, along with the digestion problems for other foods and a host of other problems from joint pain to migraines. From Wheat Belly:

Gluten is only one of the reasons to fear wheat, since it triggers a host of immune diseases like celiac, rheumatoid arthritis, and gluten encephalopathy (dementia from wheat).

The protein unique to wheat, gliadin, a component of gluten proteins, is odd in that it is degraded in the human gastrointestinal tract to polypeptides (small proteins) that have the ability to cross into the brain and bind to morphine receptors. These polypeptides have been labeled gluteomorphin or exorphins (exogenous morphine-like compounds) by National Institutes of Health researchers. Wheat exorphins cause a subtle euphoria in some people. This may be part of the reason wheat products increase appetite and cause addiction-like behaviors in susceptible people. It also explains why a drug company has made application to the FDA for the drug naltrexone, an oral opiate-blocking drug ordinarily used to keep heroine addicts drug-free, for weight loss. Block the brain morphine receptor and weight loss (about 22 pounds over 6 months) results. But there’s only one food that yields substantial morphine-like compounds: yes, wheat.

The complex carbohydrate unique to wheat, amylopectin A, is another problem source. The branching structure of wheat’s amylopectin A is more digestible than the amylopectins B and C from rice, beans, and other starches (i.e., in their natural states, not the gluten-free dried pulverized starches). This explains why two slices of whole wheat bread increase blood sugar higher than table sugar, higher than a bowl of brown rice, higher than many candy bars. Having high blood sugars repeatedly is not good for health. It leads to accumulated visceral fat–a “wheat belly,” diabetes and pre-diabetes (defined, of course, as having higher blood sugars), not to mention cataracts, arthritis, and heart disease.

As if that wasn’t enough, there are even other components of wheat that are harmful, such as the lectins in wheat. Lectins are glycoproteins that have the curious ability to “unlock” the proteins lining the human intestinal tract that determine what substances can enter the blood or lymphatic system and what substances cannot. The intestinal tract must be selective in what is allowed to enter the human body else all manner of diseases can be triggered, especially autoimmune diseases. Wheat lectins disable these proteins. This is the suspected explanation for why wheat consumption has been linked to rheumatoid arthritis, skin diseases like dermatitis herpetiformis, Hashimoto’s thyroiditis, and a variety of other inflammatory diseases.

Beyond gluten, there are over 1000 other proteins in wheat that also have potential for odd or unexpected responses. You might say that wheat is a perfectly crafted Frankengrain that almost appears like it was created to exert maximum health damage in the most desirable, irresistible form possible. I really don’t believe that this monster was created on purpose to hurt people, but the astounding collection of adverse effects, all packed into one food, pushed on us by the U.S. government and other “official” health agencies, explains why this one thing has exerted more harm than any foreign terrorist group can inflict on us.