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Q: What should I eat and drink to get a better night’s sleep? I see all sorts of sleep-promoting diets on the Internet.

A: Other than alcohol and caffeinated beverages, no food or beverage has a clear-cut effect on sleep.

Theories about food and sleep involve such factors as blood sugar levels, hormones, and various brain chemicals. High-carbohydrate foods are often suggested for sleep, because they are supposed to allow more tryptophan (an amino acid) to get into the brain; tryptophan is converted into the brain chemical serotonin, which helps promote sleep. In contrast, a high-protein diet supposedly has the opposite effect. A high-fat diet also tends to result in poorer sleep, at least according to one recent study.

Despite common beliefs about various foods—turkey or warm milk as sleep promoters, for example—research has come up with confusing and contradictory results. Foods (and meals) are complex mixes of nutrients that may have opposite effects on sleep, and the effects may vary from person to person, possibly for genetic reasons.

According to Dr. William Orr, an expert on sleep at the Oklahoma University Health Science Center, “I am not aware of studies showing the effectiveness of a specific diet promoting sleep. There’s nothing across the board that’s convincing.”

Here’s some obvious advice if you’re having trouble sleeping:

• Don’t eat a large meal two to three hours before going to bed. A full stomach can be uncomfortable and can promote heartburn. If spicy or fatty foods (or some other food) seem to cause nighttime heartburn, don’t eat them in the evening.

• Avoid, or at least limit, alcohol. It can help you fall asleep more quickly, but later it disrupts sleep, especially restorative deep sleep.

• Avoid caffeine for at least three hours before going to bed. Some people may need to avoid it for eight hours before bedtime.

Q: Does grape juice have the same health benefits as red wine?

A: Some of the benefits, probably. Much of the heart benefit of wine and other spirits comes from the alcohol itself, which boosts HDL (“good”) cholesterol and has anti-clotting effects. However, studies using de-alcoholized red wine and grape juice suggest that wine’s protective effects go beyond its alcohol: some may also come from anti-oxidant compounds in the grapes, called polyphenols.

For example, a small study from Boston University School of Medicine several years ago found that people with heart disease who drank about two cups of purple grape juice a day for two weeks had an increase in HDL and a decrease in two markers of inflammation. Other research has shown that grape juice reduces oxidation—and thus the artery-damaging effects—of LDL (“bad”) cholesterol. And like wine, both grape juice and de-alcoholized red wine increase nitric oxide, which improves blood vessel functioning.

Polyphenols, including resveratrol and anthocyanidins, are concentrated in the skin and seeds of red and purple grapes. Thus they are present in red wine and grape juice, since both are made from crushed whole grapes. Depending on the grape variety, growing conditions, and processing, however, wine and grape juice vary greatly in their polyphenol content. In contrast, white wine, made from only the flesh of red or green grapes, contains little or no resveratrol and anthocyanidins, but has other potentially beneficial substances.

To get the most from grape juice, choose one made from 100% red or purple grapes. A downside is that it is high in calories—150 per cup, more than most juices, but less than wine. Grapes themselves are a less concentrated source of polyphenols, especially if you don’t eat the seeds. Another option is alcohol-free wine, which usually has only 20 to 40 calories in 5 ounces.

UC Berkeley Wellness Letter, April 2009