Anyone who has struggled with obesity their entire life—cutting calories, exercising—may wonder why they still can’t lose weight. That’s because, according to Dr. Jason Fung, a practicing kidney specialist in Toronto, Canada, the physiology of obesity is far more complex than “eat less and move more.”
In his 2016 bestseller, which sold millions of copies, fat code, He believes obesity is a hormonal imbalance rather than a caloric imbalance, as chronically high insulin levels prompt you to store fat. He has now written another excellent and illuminating science book, The Hunger Code: Resetting the Body’s Fat Thermostat in the Age of Ultra-Processed Food, In it he reveals the secrets to long-term weight loss and improved health. They might surprise you.
It’s not the calories you eat, it’s the calories you store
Dr. Feng doesn’t claim that calories don’t matter at all. He believes that weight loss or gain is not as simple as the basic math of calories in and calories out. It’s “too easy,” he said.
What really matters, he believes, is how your body processes those calories—how much of what you eat is burned or stored as fat. “Every weight loss study shows that when you count calories and eat less, your basal metabolic rate (i.e. the number of calories you burn) goes down. So you can eat less, but you’ll burn Less, too, so the weight is still not lost,” he said.
Fung cited three large studies, including the Women’s Health Initiative, in which participants reduced their calorie intake by 371 and increased physical activity by 10 percent. “Exercise, while beneficial to health, does not increase calorie burn because the body compensates by slowing metabolism after exercise,” he points out. At the same time, he reported that after seven years of dieting, “they weighed no less than the women in the study who didn’t change their diet at all.”
Dr. Feng says it’s not just the number of calories that matters, but how your body uses them – Bernard Okulaja Photography
Again, it’s your body that matters Do with your calories. “For every calorie you eat, your body can either store it or burn it. So it’s not just the number of calories that matters. If your body stores it, you get fat. If it burns it, you don’t get fat.”
Which one of these depends on what you eat. Think in terms of “good calories” and “bad calories.” Treating all calories equally is the secret to weight gain. Most of us know that some foods are more fattening than others, Feng said. A 200-calorie cookie is more fattening than a 200-calorie carrot. but why? Because, he says, besides calories, all food contains the body’s “information.” The key to losing weight (or gaining weight) is which hormones are stimulated by what you eat.
Hormones make you hungry
The most important factor in determining our weight is hormones. The GLP-1 hormone tells us to feel full. Ghrelin tells us to be hungry. Leptin tells us to lose body fat. The hormones insulin and cortisol tell us to store body fat. So if you eat something that stimulates insulin in large amounts, you will gain weight.
“If you eat an 800-calorie, three-egg veggie omelet for breakfast, you’ll be full. That will carry over to lunch and even dinner. If you drink an 800-calorie Starbucks Frappuccino, you’ll be hungry five minutes later,” Fung explains. The calorie content is the same, but the two portions are completely different. “Why? Because they stimulate different hormones. Every food you eat contains calories, but it also contains instructions and information about how your body processes those calories.”
When you eat a vegetable omelet, it doesn’t stimulate as much insulin, he says. “So most of the calories can be used as energy for the body.” Therefore, GLP-1 is released, telling us that we are full. “But after you drink a Frappuccino, your insulin spikes like crazy, and all those calories are immediately stored as body fat, so your body has no energy.” Your blood sugar will drop, and your body will understandably signal hunger by releasing a surge of ghrelin. “After five minutes, you’re like ‘I need to eat something,'” he said. “It’s hormones, not calories, that ultimately determine whether you gain weight.”
Meal time is also important. Even if you eat the exact same meal in the morning and evening, “they can have very different effects on insulin levels,” says Feng, which makes perfect sense. “What insulin does is tell you to store fat, so if you eat late at night, your insulin levels will be about 25 percent higher than in the morning. That’s because you’re going to bed, so your body is thinking, ‘What do I do with all these calories? I should store them,’ whereas in the morning, it knows you just woke up and may need energy for the day ahead.”
Eggs and vegetables are among the foods included in a low-insulin diet
The order of meals also affects the amount of insulin released. Eat fish and vegetables before pasta, and eggs before toast – because fiber, fat and protein don’t stimulate much insulin, eating them first slows down your digestion and absorption of carbohydrates, meaning less insulin is stimulated.
Avoid eating only carbs, which Feng calls “naked carbs.” “For example, if you eat white bread and jam, then those are pure carbohydrates, which are glucose.” This means it is quickly digested and absorbed, which increases insulin levels. He cited experiments in which participants ate two meals, “bread and orange juice, and then 10 minutes later, chicken and vegetables—or you flip it around, chicken and vegetables, and then 10 minutes later, bread and orange juice. When you eat carbs at the end, insulin levels drop by 50 percent.”
Foods on a low-insulin diet include meat and poultry, fish, eggs, cheese, full-fat yogurt, nuts and seeds, vegetables, beans, legumes, fermented foods, fruits (low in fructose like berries), healthy fats and spices.
How to permanently reset your fat thermostat
As Dr. Feng said in the book hunger code, Our bodies automatically keep all key systems (including hydration, temperature, blood oxygen levels, and body fat) in balance. These are its “homeostatic mechanisms.” The amount of fat we carry in our bodies is set by our body’s “fat thermostat” at a sweet spot called the “body set weight.” This is because, “just like wild animals, body fat remains relatively constant despite varying conditions” to optimize survival, and we don’t mean to be extremely thin or fat.
“The amount of fat in our bodies is tightly controlled,” Feng explains. If it’s too high or too low, our bodies adjust, raising or lowering our hunger levels to reset it, which then slows or speeds up our metabolism. Or should. Obesity is “a disease in which the body’s set weight is too high.”
So how does our fat thermostat get out of control? “There are hormones that push it up” — insulin, cortisol — “and there are hormones that push it down,” Feng said. “If you stimulate GLP-1 like the Ozempic and Mounjaro weight loss shots do, you’ll lose weight.”
Thicker smoothies containing seeds are more satiating than thin liquids such as juices or carbonated drinks – Moment RF
The GLP-1 hormone affects fat levels indirectly by increasing or decreasing feelings of hunger or fullness. A diet composed primarily of processed foods and refined carbohydrates can cause insulin to rise, leading to hunger, overeating, and weight gain. It can lead to insulin resistance—the need for increased amounts of insulin to clear blood sugar after eating—leading to chronically high insulin levels. This “keeps pushing the thermostat up,” Feng said. Then, when your body defends this high set point, it becomes difficult to maintain weight loss.
Other hormones also affect our weight and tendency to store fat. Higher levels of testosterone prompt the body to build muscle and burn fat, which explains why teenage boys can eat 5,000 calories a day (“They’ll clean out your refrigerator!” exclaims Fung, who has two sons, ages 19 and 22) and not gain fat. Why? “Because hormones direct those calories to be burned.”
At the same time, estrogen is an appetite suppressant, so perimenopause (when estrogen fluctuates and declines) is “a woman’s highest risk period for weight gain,” Feng says. “When you have less estrogen in your body, you tend to eat more. This causes your body temperature to rise.” If you try to beat it by cutting calories, your body will “lower your metabolic rate.”
So what can you do? What you eat (or don’t eat) is key. “Fasting is actually a very good way to achieve this [thermostat] down. “You turn off food and try to lower insulin levels,” he says. This forces the body to burn fat for fuel.
Feng recommends a low-carbohydrate, high-fat diet—a “low-insulin diet”—plus intermittent fasting to lose weight and keep it off. He admits, “I actually have a tendency to put on weight” – but on his own advice, he recently put on a pair of green trousers from 25 years ago. “They were terrible, but I put them on anyway. My wife was not impressed!”
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