Human beings have survived for millennia because most of us make good decisions about our health most of the time.

As an undergraduate at Harvard in the 1960s, I was fascinated by my visits to psychologist B.F. Skinner's laboratory.

The usual justification for eating extra meals is that it keeps the metabolism "revved up" so that weight loss is easier. There is, however, very little hard evidence that supports this idea, and a fair amount that disputes it.

Studies have shown that people who are physically active sleep better than those who are sedentary. The more energy you expend during the day, the sleepier you will feel at bedtime.

People who are contented and serene sleep well. They fall asleep easily, stay asleep, and wake refreshed. Conversely, people who are anxious, stressed, or depressed do not sleep well, and chronic insomnia is strongly associated with mood disorders. These are clear correlations, but what is cause and what is effect is not clear. Most experts agree that sleep and mood are closely related, that healthy sleep can enhance emotional well-being, while insufficient quantity or quality of sleep can adversely affect it.

My personal opinion is that the neutral position on the mood spectrum—what I called emotional sea level—is not happiness but rather contentment and the calm acceptance that is the goal of many kinds of spiritual practice.

Fear and greed are potent motivators. When both of these forces push in the same direction, virtually no human being can resist.