Fat metabolism is the most efficient way to produce energy, allowing you to go and go and go without burning through a ton of calories. But efficiency is the enemy of fat loss. To lose body fat, you want to churn through calories—calories from carbs, calories from fat, calories from anything—and you get there through carb metabolism. “The more energy-demanding the work, the more likely you are to lose body fat,” Zimmerman explains.
Women who wake up and go to bed at the same time each day have lower levels of body fat, according to a study of more than 300 women from Brigham Young University in Utah. Chaotic sleep habits cause your internal clock to go haywire, which in turn causes your body to secrete fat-storing hormones like cortisol. The sweet spot? Try not to stray an hour from your usual sleep pattern, the study authors say. More than a 90-minute difference in sleep and wake times were linked to more body fat. (Tossing and turning? Check out these 100 tips to sleep better every night.)
Don’t let extra hours lounging in bed stand between you and a flatter belly. While getting enough sleep can help boost your metabolic rate, sleeping in may undo any benefit you’d enjoy from catching a few extra winks. One study reveals that late sleepers who snoozed past 10:45 in the morning ate nearly 250 more calories over the course of the day, despite eating half as many fruits and vegetables as their early bird counterparts. Even worse, they chowed down on more salty, sugary, and trans fat-laden fast food than those who woke up earlier. If you happen to head out of the house early, you’re in for an additional metabolic boost; researchers at Northwestern University have found that people exposed to just a short period of early morning sunlight had lower BMIs than their late-waking counterparts.
When a lot of insulin is released by the body consistently throughout the day, not only does it prevent fat loss, but it also encourages the body to store energy as body fat. The types of calories that spike insulin the most are those from carbohydrates in the form of simple sugar. So if you want to eat carbohydrates, stick to healthy carbohydrates from food that gets digested slowly. Along with carbohydrates, protein can also spike your insulin levels, especially those from dairy-based sources like skim milk and yogurt.
Carbs are always perceived as the enemy, but they too have a significant role in fat loss. The body needs glucose to work, and to a certain level, your brain requires it to think and function optimally. Some will argue that technically we don't need carbs, but many of your body's basic functions will decrease in performance without the right amount of carbs at the right times.
Cut back on carbs: Remember how insulin has the biggest impact on fat storage? Well, carbs have the biggest impact on insulin. ”Too many carbohydrates leads to a spike in the hormone and then to more fat storage,” Seedman explains. Not only should you cut back on carbs, but your insulin will spike even more from processed ones, so cut any carb that’s not a whole grain or from real produce completely. And don’t worry: Carbs are traditionally thought of as your body’s main source of energy, but your body also has the ability to fuel from fat, so if you’re increasing your fat and protein intake, your body doesn’t need as many carbs to run. You still need some amount of carbohydrates to regulate certain biological processes, like your muscles’ ability to stay hydrated and maintain structural integrity, so don’t cut the macronutrient completely, Seedman warns. For a high-fat, low-carb diet, aim for at least .5 of your bodyweight (so a 200 lb person would eat at least 100 grams of carbs per day), he suggests. For a more balanced calorie-restricted diet, that number jumps to .75 to 1.5 grams per pound of bodyweight.
What about the calories? When they avoided eating between the hours of 7 p.m. to 6 a.m., participants reduced their daily calorie intake by an average of 238 calories. Which helps to explain the weight loss of almost half a pound a week. Interestingly, their intake of fat decreased significantly while protein and carbohydrate decreased at a more conservative rate. This leads one to believe that the subjects were not eating grilled chicken and broccoli late at night. No, their usual late-night snacks were much higher in fat.
That said, a Medicine & Science in Sports & Exercise study found that runners lost more weight than walkers over a six-year period, possibly because of the afterburn effect. “Running at a high intensity will create an afterburn, which is when your body continues to burn calories when you’re no longer moving,” Rubin says. She suggests starting with three 30-minute runs a week, sprinting for 30 seconds then recovering for 30 seconds to a minute.
At its core, burning fat comes down to the process of lipolysis—the breaking down of fat lipids, explains Seedman. This happens in the mitochondria of the muscles, or the powerhouses of the cells, responsible for generating the energy our cells need to do their jobs. Exercise has been shown to improve mitochondria function, which then promotes fat breakdown, Seedman adds. Plus, working out helps regulate pretty much all the hormones that optimize fat loss.