A number of well-known nutritionists have said something similar to this: that the obesity epidemic in the U.S. has occurred not from belt-loosening pig-outs but from minor miscalculations. A few go so far as to say that the epidemic would end abruptly and the collective health of America would improve radically if Americans simply consumed 100 fewer calories a day.

That's not much food at all.

It's one less slice of lightly buttered bread a day. Or 4 teaspoons of standard salad dressings, 4 chocolate kisses, 8 ounces of most sodas, 10 pretzel sticks, 15 jelly beans, or a handful of potato chips.

But if that's really the case, why hasn't our use of caffeine already corrected this?.

The difference between consuming 2100 calories a day instead of 2000 is an excess of 4.7 percent and research published in a 2010 issue of the International Journal of Obesity found that ingesting caffeine something that more than 75 percent of Americans do regularly increases metabolic rate by 4 to 5 percent.

So why doesn't a cup of joe cancel out Joe's minor dietary mistakes? One reason is that the average Joe does more than make minor mistakes. He also underestimates caloric consumption by about 25 percent.

But this does not mean that caffeine can not aid the weight-loss process. Quite the contrary. Caffeine is found in the majority of products sold as weight-loss supplements.

Use any of these products according to their prescribed directions, and you should increase your basal metabolic rate by 4 to 5 percent, which has been enough to produce a 2-to-4 pound weight loss in clinical trials. (Be suspicious, however, of products that add other caffeinelike ingredients that claim greater success. This has not been substantiated in research.)

But using caffeine as a daily aid in your attempt to create weight loss may not be the most effective use of it. If you limit your ingestion of caffeine to once every three or four days in two relatively small 75 mg doses about 6 ounces of brewed coffee, 8 ounces of Red Bull, or 12 ounces of Pepsi Max before tougher than typical workouts, you'll get far more out of the stimulant and yourself than you might imagine.

That's because using caffeine in the previously mentioned way will do more than just increase your BMR. It will allow you to work harder and longer during your workouts as well as burn a higher percentage of fat.

But a key to this is avoiding the stuff most days. Research shows that it takes only four days of regular caffeine ingestion to develop a tolerance to it, which means you lose that caged-lion feeling at the start of your workout.

That's because the receptors in your body that caffeine stimulates increase in number with daily use. More receptors means you need more caffeine to create the desired effect.

So daily use either means that you lose that effect or increase the dose to a degree that increases the chance of adverse health reactions, like acid reflux, withdrawal headaches, heart palpitations, and ulcers. Equally as significant is that heavy caffeine use can not only disrupt your sleep patterns, creating chronic fatigue, but also affect the hormones that regulate your appetite, formulating that frantic type of hunger that foils even the most fervent dieter.

Since the half-life of caffeine is 6 hours, it takes at least 30 hours to completely leave your body. Add another day or two for your nervous system to do something the docs call deregulate, and three days of abstaining from caffeine is what you need to foster that turbocharged feeling before a workout.

That turbocharged effect peaks when blood levels of caffeine peak about 45 to 60 minutes after you ingestion, but you should take your first dose of caffeine at least two hours before that. Research has shown that's the length of time needed for caffeine to maximally perform another job that aids your workout and also weight loss: fat breakdown.

Caffeine causes some stored fat to be released into the blood stream for energy. While your body prefers to burn glycogen (the energy that comes from carbohydrates) to fuel workouts, ingesting caffeine three hours before a workout can increase the percentage of fat used along with glycogen.

Since fat can only be effectively utilized as energy while the body is still burning some glycogen whether it comes from energy stores early in a workout or a gel or a drink later sparing glycogen early in a workout, which is what caffeine does, allows you to work out longer and harder.

Longer and harder means that you not only burn more calories during your workout but also more after, a result of something called afterburn.

In a study led by Carol A. Binzen, a clinical exercise physiologist at Johns Hopkins University, women burned on average 50 additional calories in the two hours after 40 minutes of aerobics, or 50 calories more than their typical basal metabolic rate while at rest. Women who lifted weights burned an average of 155 calories in the two hours of rest immediately afterwards.

Although there's some disagreement about this, the afterburn effect seems to increase significantly as the duration or intensity increases, making a 90-minute once or twice a week especially helpful for weight loss.