 I hear from lots of people every day who are concerned about how their diet is affecting their health. They need answers based on facts—in other words, from the peer-reviewed medical literature—and that is what I'm here for. Welcome to the Nutrition Facts Podcast. I'm your host, Dr. Michael Greger. Today we do the math on how many fewer calories we have to eat every day to lose one pound of body fat. The first surgical attempt at body sculpting was in 1921 with a dancer wanting to improve the shape of her ankles. The surgeon apparently scraped away too much tissue and tied the stitches too tight, resulting in necrosis, amputation, and the first recorded malpractice suit in the history of plastic surgery. Today's liposuction is much safer, only killing about 1 in 5,000 patients. Mostly from unknown causes, throwing a clot off into your lung or perforations of your internal organs. Liposuction currently reigns as the most popular cosmetic surgery in the world, and its effects are indeed only cosmetic. A study published in the New England Journal of Medicine assessed obese women before and after having about 20 pounds of fat sucked out of their bodies, resulting in nearly a 20% drop in their total body fat. Normally, you lose even just 5-10% of your body weight in fat, and you get significant improvements in blood pressure, blood sugars, inflammation, cholesterol, and triglycerides, but liposuction sucks. None of those benefits materialized even after the massive liposuction. This suggests subcutaneous fat. The fat under our skin is not the problem. The metabolic insults of obesity arise from the visceral fat. The fat surrounding or even infiltrating our internal organs, like the fat marbling our muscles and liver. The way you lose that fat, the dangerous fat, is to take in fewer calories than you burn. Anyone who's seen the biggest loser shows knows with enough calorie restriction and exercise, hundreds of pounds can be lost. Similarly, there are cases in the medical literature of what some refer to as super-obesity, in which individuals lost up to 374 pounds largely on their own without professional help and kept it off for years. The guy lost about 20 pounds a month cycling two hours a day and reducing intake to 800 calories a day, which is down around what some prisoners were getting at concentration camps in World War II. Perhaps America's most celebrated TV weight loss was when Oprah pulled out a wagon full of fat representing the 67 pounds she lost on a very low calorie diet. How many calories did she have to cut to achieve that within four months? Consult-leading nutrition textbooks or refer to trusted authorities like the Mayo Clinic and you'll learn the simple weight loss rule. One pound of fat is equal to 3,500 calories. Quoting from the Journal of the American Medical Association, a total of 3,500 calories equals one pound of body weight. This means if you decrease your intake by 500 calories daily, you will lose one pound per week, 500 calories per day, times 7 days equals 3,500 calories, so one pound of body fat. The simple weight loss rule, that's simply not true. The 3,500 calorie rule can be traced back to a paper in 1958 that just noted that since fatty tissue on the human body is 87% fat, a pound of body fat would have about 395 grams of pure fat. Multiplying that by 9 calories per gram of fat gives you that 3,500 calories per pound approximation. The fatal flaw that leads to dramatically exaggerated weight loss predictions is that the 3,500 rule fails to take into account the fact that changes in the calories inside of the energy balance equation automatically lead to changes in calories out. For example, the slowing of metabolic rate that accompanies weight loss known as metabolic adaptation. That's one of the reasons weight loss plateaus. For example, imagine a 30-year-old sedentary woman of average height who weighs 150 pounds. According to the 3,500 calorie rule, if she cuts 500 calories out of her daily diet, she'd lose a pound a week or 52 pounds a year. In three years then, she would vanish. She'd go from 150 pounds to negative 6. Obviously, that doesn't happen. What would happen is that in the first year, instead of losing 52 pounds, she'd likely lose only 32 pounds. And then, after a total of three years, stabilize at about 100 pounds. This is because it takes fewer calories to exist as a thin person. Part of it is simple mechanics. In the same way a Hummer requires more fuel than a compact car, think how much more effort it would take to just get out of a chair, walk across the room, or climb a few stairs carrying a 50-pound backpack. That's no lighter than carrying 50 pounds in the front. Even when you're lying at rest sound asleep, there's simply less of your body to maintain as we lose weight. Every pound of fat tissue lost may mean one less mile of blood vessels. Your body has to pump blood through every minute. So the basic upkeep and movement of thinner bodies takes fewer calories. So as you lose weight by eating less, you end up needing less. That's what the 3,500 calorie rule doesn't take into account. Or imagine it the other way. 200-pound man starts eating 500 more calories a day. That's like a large soda or two donuts. According to the 3,500 calories rule in 10 years, he'd weigh more than 700 pounds. That doesn't happen because the heavier he is, the more calories he burns just existing. If you're 100 pounds overweight, that's like the skinny person inside you trying to walk around balancing 13 gallons of oil at all times, lugging around a sack containing 400 sticks of butter wherever you go. It takes about two donuts worth of extra energy just to live at 250 pounds. And so that's where he'd plateau out if he kept it up. So weight gain or weight loss, given a certain calorie excess or deficit, is a curve that flattens out over time rather than a straight line up or down. Nevertheless, the 3,500 calorie rule continues to crop up, even in obesity journals. Public health researchers used it to calculate how many pounds children might lose every year if, for example, fast food kids' meals swamped in apple slices instead of french fries. They figured two meals a week could add up to about four pounds a year. The actual difference, National Restaurant Association funded researchers were no doubt delighted to point out, would probably add less than half a pound, 10 times less than the 3,500 calorie rule would predict. The original article was subsequently retracted. In our next story, we try to understand the metabolic and behavioral adaptations that slow weight loss. We have millions of years of evolution hardwiring us to survive scarcity. Compensatory survival mechanisms our body uses to defend against weight loss. So when we start losing weight, we may unconsciously start moving less as a behavioral adaption to conserve energy. There are metabolic adaptations as well. Our metabolism slows down. Every pound of weight loss may reduce our resting metabolic rate by seven calories a day. This may only translate to a few percent differences for most, but can rapidly snowball for those who achieve massive weight loss. During one season, some of the biggest loser contestants famously had their metabolic rates tracked. Above and beyond the hundreds of calories less it takes to just exist 100 plus pounds lighter. By the end of the season, their metabolic rate slowed by an extra 500 calories a day. The mind-blower was that six years later they were retested and still had the 500 calorie a day handicap. So the contestants had to cut 500 calories more than anyone else their size to maintain the same weight loss. No wonder the bulk of their weight was regained. Most remained at least 10% lower than their starting weight though, and even a 7% drop has been shown to cut diabetes rates about in half. Still, the metabolic slowing means you have to work that much harder than everyone else just to stay in place. Analyzing four seasons of the biggest loser minute by minute, researchers noted that 85% of the focus was on exercise rather than diet, though the exercise component accounted for less than half of the weight loss. Even six years after their season ended, the contestants had been maintaining an hour of daily, vigorous exercise, yet still regain most of the weight. Why? Because they started eating more. They could have cut their exercise to just 20 minutes a day and still maintained 100% of their initial weight loss if they would have just been able to keep their intake under 3,000 calories a day. That may not sound like much of a challenge, but weight loss doesn't just slow your metabolism, it boosts your appetite. If it were just a matter of your weight settling at the point at which your reduced calorie intake matches your reduced calorie output, it would take years for your weight loss to plateau. Instead, it often happens within six to eight months. You may know the drill. Start the diet, stick to the diet, and then weight loss stalls six months later. What happened? Don't blame your metabolism. Just plays a small part. What happened is that you likely actually stopped sticking to your diet because your appetite went on a rampage. Let's break it down. If you cut 800 calories out of your daily diet, 2,600 calories a day down to 1,800, and your weight loss stalls after six months, then what happened is that at the end of the first month you think you're still cutting 800 calories, but you may actually only be down about 600 calories a day. By month two, you're only down about 500, month three, 300, and by month six, you're only eating 200 calories less than before you went on the diet. In other words, you inadvertently suffered an exponential increase in calorie intake over those six months. Yet you may not even realize it, because by that time your body may have ramped your appetite up 600 calories, so it still feels as though you're eating 800 calories less, but it's actually only 200. Since an 800 calorie drop in intake may slow your metabolism and physical activity about 200 calories a day, with no difference between calories in and calories out at six months, no wonder your weight loss grinds to a complete halt. The slow upward drift in calorie intake on a new diet is not because you got lazy. Once your appetite is boosted by 600 calories after dieting for a while, eating 200 calories less at the end is as hard as eating 800 calories less at the beginning, so you can maintain the same disciplined level of willpower and self-control and still end up stagnating. To prevent this from happening, you need to maintain the calorie deficit. How is that possible in the face of a ravenous appetite? Hunger is a biological drive. Asking someone to eat smaller portions is like asking someone to take fewer breaths. You can white-knuckle it for a bit, but eventually nature wins out. That's why I wrote How Not To Diet. There are foods that can counter the slowing of our metabolism and suppress our appetite. Ways of eating to counter the behavioral adaptation and even eat more food, yet still lose weight. Due to the metabolic slowing and increased appetite that accompanies weight loss, sustained weight loss requires a persistent calorie deficit of 300 to 500 calories a day. This can be accomplished without reducing portion sizes simply by lowering the calorie density of meals. This can result in the rare combination of weight loss with both an increase in quality and even quantity of food consumed. The bottom line is that sustainable weight loss is not about eating less food, it's about eating better food. For testimonials, we may be able to share it on social media to help inspire others. If you see any graphs, charts, graphics, images, or studies mentioned here, please go to the Nutrition Facts Podcast landing page. There you'll find all the detailed information you need, plus links to all the sources we cite for each of these topics. My latest book, How Not To Age, is out now, premiering at number two on the New York Times best-sellers list. Check it out at your local public library, and of course all the proceeds of the sales of all my books goes directly to charity. NutritionFacts.org is a non-profit science-based public service where you can sign up for free daily updates on the latest nutrition research with bite-sized videos and articles. Everything on the website is free, there are no ads, no corporate sponsorships, no kickbacks, strictly non-commercial. I'm not selling anything, I just put up as a public service, as a labor of love as a tribute to my grandmother, whose own life was saved with evidence-based nutrition.