The good news is that yoga can help one lose weight. The bad news is that the mechanism by which this occurs isn’t what most people expect, and it involves the mind a great deal more than the muscles.

While many people hope for a secret to weight loss, there’s no secret. Weight loss is a function of calories eaten being less than calories burned.  This simple formula means that one can either eat less or exercise more. Both the diet and exercise matter for good health, but the eating part is more important to cutting weight. This statement may be controversial and seemingly gratuitous—particularly for people who think exercise is going to single-handedly shed excess pounds–and so I’ll take some time to try to make my point.

The first thing one should know is that our voluntary activity only accounts for about one-third of calories consumed. The other two-thirds are used whether we move a muscle or not. Between 20 and 25% of our energy consumption is devoted to our brain, and much of the rest is used to keep us at 37°C (98.6°F) because we are, after all, mammals. This means that increasing the intensity or amount of exercise—while it has tremendous health benefits—will achieve only a marginal increase in calories burned. From the Mayo Clinic website, I learned that a 109kg (240lb) individual will burn about 273 calories doing a typical hata yoga class or about 436 calories with Power Yoga. (Compare this to about 327 calories / hr. for tai chi or 654 calories / hr. for hiking.) So your hour of yoga has maybe knocked off a 32oz soft drink or one medium size French fries. Most people have trouble finding more than one hour of time and energy for exercise per day. And as someone who sometimes spends more than an hour a day exercising, I can attest that there is a point of diminishing marginal returns. So while exercise is an important part of weight loss, one can’t go hog-wild in eating just because one exercises.

[One should also note that many yoga practitioners experience a reduced basal metabolic rate (BMR) because of the calming aspect of the practice. A lower BMR means that you burn fewer calories just living and maintaining your metabolism. All things being equal, this makes cutting weight all the more challenging—though the effect is certainly counterweighted by the stress reduction aspect of the practice that will be discussed below.]

To summarize: unless you’re an elite athlete in training for something like the Olympics, the idea that you can eat whatever you please and cut / maintain a healthy weight is likely to result in disappointment.  A common piece of dietary advice for elite athletes is to daily eat one gram of protein for every pound of ideal bodyweight and eight fist-sized servings of vegetables. Beyond that, they can pretty much eat what they want. But with that much slowly digesting material, they’re probably not going to go overboard—even if they weren’t already, almost by definition, very disciplined people.

So if an hour of yoga a day doesn’t even make up for having a Mars bar, what good is it?  For one thing, the yoga student has the opportunity to become more attuned to his or her body and, in doing so, to learn to differentiate physiological hunger from the many other permutations of hunger that overtime merge into a multi-headed hydra of craving. What are these other hungers? First and foremost, there’s psychological hunger, or the use of food as therapy. People use food to reward themselves, to medicate themselves, to take their minds off of their woes. Secondly, there’s sensory hunger in which we have no real need to eat but the food looks or smells too good to avoid.

One of the forms of hunger that often remains hidden is social hunger. That is, one eats to be part of the in-group and to bond. For example, imagine you’ve just eaten, are not hungry, and someone offers you food. Depending upon who it is and what your relationship is that person, you may feel compelled to eat even if you don’t need it. The double whammy is that eating as socializing is so deeply engrained and that we humans—contrary to popular belief—are dismal at multitasking. We can’t converse and be aware of what we are eating, and thus one may overeat because one is so engrossed in the distraction of socializing. This isn’t to say that there is anything inherently wrong with social eating. We all have to do it to some degree or another. One just needs to recognize that if it becomes a habit to be distracted from one’s food, one may have problems.

Relating back to the idea of psychological hunger, yoga helps one destress.  Stress can be a perfectly healthy phenomenon, but when it’s prolonged it can have many adverse consequences. One such consequence is having cortisol levels remain too high, and this has the effect of ramping up the appetite. Your body has been pressed into fight or flight mode, it expects that you’re hauling ass away from a sabretooth tiger or an angry woolly mammoth mamma, and that you’ll soon need to replenish depleted energy stores. Your endocrine system doesn’t know that you’re curled up on the couch with a pint of ice cream… yeah, let’s call it a “pint.” As a form of exercise, yoga helps reduce this problem. However, beyond exercise, yoga offers many relaxation techniques such as yoga nidra, kaya sthairyam, restorative postures, and some forms of pranayama(breathing exercises) that can help you turn off the “fight or flight” and turn on the “rest and digest”—what Herbert Benson called the “relaxation response.” Sometimes you might delve into an intense practice like Ashtanga Vinyasa or Power Yoga, and other times restorative yoga might be just what the doctor ordered. [Disclaimer: “What the doctor ordered” is a figure of speech. I’m not a doctor, and I haven’t even played one on TV.]

There is yet another way in which yoga can help. Yoga helps one dispassionately observe one’s drives and this way one can slowly, over time, rewire one’s attitudes toward food.  One can begin to think of hunger pangs as a sensation, rather than projecting a negative connotation onto them. In this way, one can learn to begin to watch the sensation and learn from it rather than running for the food.

Finally, an important benefit of yoga is in teaching one to be contented with oneself, even if one isn’t content to live with one’s present health or physical capability. Santosa is one of the niyama, and it teaches one to be content with who one is–perhaps even while one is simultaneously practicing the austerities of tapas (another niyama) in pursuit of personal development. If one isn’t contented with oneself, one can fall into a shame spiral that may create the kind of persistent stress that I warned about above. Also, if one is at a healthy weight, but has some deep-seated drive toward “perfection,” the lessons of santosa can inform you as well.

Best of luck in the pursuit of good health.