For example, when it comes to hormones, ghrelin makes you hungry, leptin and other hormones keep you feeling full, Nadolsky says. Thyroid, cortisol, insulin, testosterone, and estrogen all influence how you metabolize and store energy. Meanwhile, genetics have a large influence on both basal metabolic rate (how many calories you burn just to live) and hormone health. While all of these things are impacted by our diet, they’re not only controlled by the way we eat. And, in fact, while sleep, stress management, and, when needed, medication can help regulate other hormone levels such as estrogen and thyroid, our hormones and other physiological processes are often out of our control. And by the way, being able to impact our hormone levels and metabolism with our diet doesn’t always work out in favor of weight loss. As a 2016 review notes, one of the reasons weight loss by way of caloric restriction isn’t efficacious is because “this strategy is countered by the body’s natural physiological response to negative energy balance.” In other words: The body fights back against caloric restriction.
Physical activity helps burn abdominal fat. “One of the biggest benefits of exercise is that you get a lot of bang for your buck on body composition,” Stewart says. Exercise seems to work off belly fat in particular because it reduces circulating levels of insulin —which would otherwise signal the body to hang on to fat—and causes the liver to use up fatty acids, especially those nearby visceral fat deposits, he says.
But his struggle resonates with lifelong dieters. For most of his life, Stevens, now 41, believed certain foods had the power to make him fat or thin. He went on his first diet at age 10, and for 25 years he counted calories, carbs and fat while on every diet from Atkins to the Zone. He lost hundreds of pounds, but they always returned, and his weight continued to climb.
Research has shown that with intermittent fasting, blood pressure is reduced, levels of sugars and fats in circulation are improved, and inflammation, an indicator of heart disease risk, can be limited. Every week there is a day when you are eating a reduced amount of calories compared to the other days, to achieve this. He has dieters follow a specific four-week eating plan, including some days where the calorie count is about 1,600, and other days where it is 900. (The average caloric intake for women is about 1,800 a day; for men, 2,500, according to government statistics).
Rather than a long and low-intensity cardio workout, try the HIIT method of cardio: intense, fast-paced intervals that leave you completely exhausted after only a 20- to 30-minute session. This form of cardio training increases the afterburn effect, allowing your body to continue burning calories long after your workout is over. You can rotate between 30 seconds of your favorite exercises, with rest in between, as long as they work different muscle groups—such as squats, push-ups and kettlebell swings.
What does a HIIT workout look like? You could jog for two minutes, sprint for one minute, jog for two minutes, sprint for one minute. Or you could do a HIIT workout on a bike, or by running up stairs and then jogging back down. The key is that you go relatively all out for a short period of time, then recover by maintaining a moderate level of intensity, then go again.
After somewhere between three and five hours, your body stops processing its last meal. There's nothing left to absorb, so insulin levels naturally decrease. Then, somewhere between eight and 12 hours after that last meal, your body starts burning stored fat. (Why don't you start burning fat sooner? Biology is sometimes a pain in the ass; it's like our bodies will do anything to hang on to fat.)
"Your body needs a healthy balance of exercise and rest. Doing too much prevents the body from shifting excess fat. Exercising without rest can impact our levels of the steroid hormone cortisol and cause an increase of stubborn fat stored in the belly. Not allowing your body to recover can increase the risk of injury too, so make sure you factor in rest days to your plan."