5.2: Some Realities of Sugar

There’s one health problem with sugar—as a cause of tooth decay. Otherwise, a major concern is that a sugar-rich diet is usually a nutritionally poor one. Typically, a sugar-rich diet is one in which soft drinks and sweets—candy, pastries, ice cream, etc.—displace more nutritious foods. Also, a high-sugar diet is usually high in fat and low in fiber as well.

Sugar and Tooth Decay

Tooth decay is a preventable disease caused by mouth bacteria. The bacteria feast on sugars and excrete an acid waste. Tooth decay results when the acid first demineralizes the enamel and then erodes it, allowing bacteria to infect the tooth (see Fig. 5-4).

Saliva is rich in calcium and phosphorus and can remineralize enamel before it erodes. When we don’t provide sugar for the mouth bacteria (between meals, etc.), the saliva returns to its non-acidic, slightly alkaline state, and can restore some of the minerals—but only at the earliest stages of mineral loss.

This is why constant snacking promotes tooth decay, and why cleaning the teeth promptly after eating helps prevent tooth decay. Sucking on hard candy throughout the day, for example, gives bacteria a steady source of sugar with which to make acid—too much time for mineral loss and not enough time for restoration.

Figure 5-4: Tooth Decay. Cross-section of tooth with decay at two common sites.

A striking example is “bottle mouth,” the rampant tooth decay seen in young children who are put to bed with a bottle of milk (milk has the sugar lactose). Children fall asleep while sucking on the bottle (or their mother’s breast), with a pool of milk in their mouths, and may also suck on the bottle intermittently throughout the night. A bottle of fruit juice or sugared water is, of course, just as bad.

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Treating severe tooth decay is not only expensive, but can be traumatic for young children.

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Children’s teeth are especially susceptible to decay; the enamel of newly-emerged teeth isn’t yet completely mineralized (“hardened”). They shouldn’t get in the habit of going to sleep with a bottle even if their teeth haven’t come in yet—habits are hard to break.

A popular classroom experiment is to dissolve a tooth in a glass of Coca-Cola, to show how sugar “rots the teeth.” Children are impressed but, actually, it’s the long-term acidity—not the sugar nor any bacteria—that dissolves the tooth in this demonstration. Vinegar (or diet Coke) would do the same thing. In the mouth, the acid made by the bacteria from the sugar is the true villain.

The bacteria don’t discriminate between sugars “artificially” added in soft drinks and sugars found “naturally” in raisins. The raisins, in fact, promote tooth decay more than soft drinks. Raisins are sticky and keep their sugars on the teeth longer, prolonging acid production.

Does Sugar Cause Hyperactivity?

Despite claims to the contrary, diet hasn’t been found in double-blind studies to cause hyperactivity, criminality, etc. (Nor have double-blind studies found such behavior to be helped by massive doses of vitamins, or dietary manipulations such as eliminating sugar.)

Double-blind studies are essential in investigating such dietary relationships, because evaluations of behavior are subjective and prone to bias. Also, dietary changes may improve behavior without the diet itself being directly responsible.

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Double-blind study: A study in which neither the subjects nor the investigators evaluating them know whether a particular subject is in the test group or the control group used for comparison.

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Severely restrictive diets drastically change the entire family dynamics. It’s thought that this change in itself can reduce a child’s hyperactivity—or its perception. More time is spent shopping for foods; meals are specially planned; and more time is spent preparing them. Children get more positive attention, and they feel better about themselves because they’re not held responsible for deviant behavior. These changes, rather than food substances, may cause the improved behavior.

Despite the popular belief that sugar causes hyperactivity and adolescent delinquency, controlled studies suggest the reverse—that sugar has a calming effect. This isn’t surprising, based on what little we know about “food and mood.”

Sugar and Mood

Does what we eat throughout a day affect our mood? As tantalizing as the question is, the scientific tools and basic knowledge needed to explore it fully are only now beginning to emerge. But what little we do know is intriguing.

The brain chemical serotonin has a calming effect; it’s made from tryptophan, one of the nine amino acids essential in our diet. Experimental animals fed tryptophan-deficient diets produce less serotonin, and become irritable, hypersensitive to pain, and develop insomnia.

Since tryptophan comes from dietary protein, one might expect that a high-protein diet would raise brain tryptophan and serotonin levels. In fact, the opposite occurs, and this takes a bit of explaining.

Protein has very little tryptophan compared to other amino acids. Since the tryptophan enters the brain in competition with other amino acids in the blood, a high-protein meal brings in more tryptophan, but it brings in even more of the other amino acids. As a result, less tryptophan gets into the brain, and less brain serotonin is produced than without the high-protein meal.

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The brain chemical serotonin is made from the amino acid tryptophan. Some antidepressants, e.g., Prozac, Zoloft, are Selective Serotonin Reuptake Inhibitors (SSRIs) that raise brain serotonin and improve mood.

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A high-carbohydrate meal or snack changes the odds in favor of tryptophan by causing a rise in insulin. (Recall that a high-carbohydrate diet raises blood sugar, which in turn stimulates the secretion of insulin.) Although insulin is best known for reducing blood glucose, insulin also reduces the amounts of certain amino acids in the blood—the amino acids that compete with tryptophan for entry into the brain. Here’s the sequence of what’s thought to happen:

1. High-carbohydrate meal
2. Increased insulin
3. More tryptophan entering the brain
4. Increased brain serotonin
5. Calming effect

This is theorized to be part of the reason why some people feel sleepy after a high-carbohydrate meal. This calming effect is also theorized to be a reason why people often find comfort (“tranquility”) in carbohydrate-rich foods (e.g., candy).