My kindergarten son is a picky eater, on the autistic spectrum. He lives mostly on carbohydrates - pasta, bread, bagels, cold cereal and rice. He is very particular about other foods: Piave cheese is always appreciated. Oakvale gouda may or may not be eaten. Panera's Swiss cheese is good, their smoked cheddar is not. He'll eat fast food chicken nuggets, but won't eat the healthier versions I've found in the grocery store. He will carefully pick his way around disliked foods or search out just the bits he likes. A bowl of macaroni and cheese with peas in it finished as a bowl of peas with cheese sauce.
I've followed the standard advice of offering different foods, never forcing him to eat anything. Since he will hold food in his mouth and then spit it into the toilet, I find the Just One Bite strategy amusing. Nothing I've read ever explained WHY he was so picky! If it was some kind of sensory aversion, I'd expect him to reject certain things universally - a taste, a texture. I never saw an explanation that made sense until I saw a reference to zinc affecting the way we taste food. Taste acuity is the technical term. Could he have a zinc deficiency?
With his highly restricted diet, any nutritional deficiency could be possible. It was worth looking into.
I shall now LINK to the handy National Institute of Health zinc fact sheet. Indeed it does list "taste abnormalities" as a known consequence of zinc deficiency. I tried looking up actual studies on zinc deficiency/supplementation and the effect on taste. It was a bizarre experience.
The first problem is that it would be unethical to induce a nutrient deficiency in a human population. I did find studies done with rats. They gave the rats a diet deficient in zinc and then presented them with three types of food: pure protein, pure fat and pure carbohydrates. They then observed what choices the rats made. The rats shifted almost completely away from the carbs and ate mostly protein. What conclusion could you draw from that? Sources rich in zinc do tend to be rich in protein and fats, so maybe they were looking for the missing nutrient in the most likely places. Zinc is also important in enzymes and enzymes are proteins, so maybe they were trying to fix their faulty metabolism?
I looked at a few other rat studies, but they were much the same - raising more questions than they answered. I went on to studies on humans. These studies were difficult to design. How can you find a population that is both mildly zinc deficient and that you can exert some control over their diets? I found two such studies. One was looking very specifically at taste acuity and used residents of a nursing facility. One group was given zinc supplementation and a control group was not. They were given taste tests (water with salt, sugar, vinegar added) at the beginning and throughout the study. The results confirmed an improved ability to taste accurately. The second was on post transplant ex-dialysis patients who received zinc supplements for a year. They actually tested for zinc levels in these patients and found that even with the supplementation that it took some of them an entire year to regain normal zinc levels.
The two study groups are quite the narrow slice of our population. A group of elderly people in a retirement home isn't too extreme, but a group of kidney transplant recipients who had been on dialysis is. The post transplant study was interesting because it showed that supplementation doesn't create an instant fix.
What does zinc do? Zinc is a small but important cog in our metabolism. A zinc deficiency doesn't create huge problems like anemia(iron et al), rickets(Vitamin D & calcium) and scurvy (vitamin C), so it doesn't get the same press. Zinc is important in enzyme production and enzymes are proteins, so it is quite logical that zinc is found in protein rich foods. Zinc is important in immune system function. Zinc is important in healthy hair and skin, which is where a fair amount of it ends up. White spots in fingernails and toenails are one indicator of a zinc deficiency.
I reviewed my son's zinc intake. Foods rich in zinc came up with two hits: cheese and fortified cereals. Of those, he was eating a bowl of cereal probably every other day. Fortunately, he will eat chewable vitamins so that gives him 25% RDA. Cereal gets it all the way to 50% RDA on the days he eats it. Only half. I went looking for a zinc supplement in capsule form. You can try to grind tablets, but it is generally difficult to grind them to powder without significant waste. I found one that was 30 milligrams zinc. It said it was 200% RDA. NIH lists the adult RDA as 11 milligrams. Whose math do you trust? For children the RDA is 5 milligrams. So thirty milligrams is six times the RDA. The Tolerable Upper Intake level is 11 grams for my son. Thirty milligrams is still three times his TUI.
The zinc powder goes into the pancakes which we eat about four times a week. I don't see any improvement in his picky eating habits. It's an experiment with a one subject and no control group. It's not stellar science and I'll not be writing it up for peer review. I did learn things about zinc, human metabolism, reading labels extremely carefully, the NIH website and The Concise Encyclopedia Of Foods And Nutrition. It was worth it.