The complex truth about weight loss and exercise

If the fad of extreme diets, reality shows on television and willpower were to some extent promote the solution of the problem, we would probably already see some change. However, obesity (characterized by excess body fat and defined as a weight exceeding 120% of the recommended weight) is a much more complex problem than can be solved with magic solutions. It is not at all easy to understand why we eat what we eat, why the body regulates weight and what is the best way to get people to change unhealthy habits. For the past twenty years, our laboratory has been involved in attempts to develop more effective methods to treat obesity and maintain a healthy weight while adhering to strict methods as much as science allows.

Many of the results we received in the research challenge the popular opinions and open up possibilities for new approaches. We have shown by example that gymnastics and physical training are not the most important thing to focus on when you want to lose weight, even though they have many other benefits, including maintaining a healthy weight. As many experts suspected and as we and others have now proven: the type of food we eat and its quantity play a more important role in determining whether we lose weight. But our research went even deeper and showed that different people lose weight more effectively when they eat different foods. This understanding allows us to create a customized weight loss plan for different people, the results of which are much better than one "one size fits all" advice.

We believe that this new understanding can improve the health of millions of people around the world. Obesity increases the risk of contracting most serious non-communicable diseases, including type 2 diabetes, heart disease, stroke and some types of cancer, which are enough to shorten the average lifespan by almost 14 years. Studies show that excessive weight, among other things, also hinders the body from fighting infections, sleeping deeply and aging properly. It's time to figure out how to fight this epidemic.

fuel utilization efficiency

Weight loss can be expressed in a simple mathematical equation: use more calories than you consume. For decades, health experts have assumed that how you create this deficit doesn't matter too much: as long as you're getting the nutrients and other essentials, you can safely lose weight through any combination of increased exercise and reduced food intake. But this hypothesis did not take into account the complexity of human physiology and psychology and therefore quickly collapsed when put to the test in real life. In fact, understanding the processes and examining the subject of weight maintenance with more scientific means required more time than expected and the involvement of experts in a wide variety of subjects.

Our first step, which began in the 90s, was to answer the basic question: How much energy is needed to fuel an average human body? It is not easy to answer this direct question. Of course, people get energy from food. But in order for people to use this energy, they have to break down the food or process it into something that can be compared to fuel in a car. The oxygen we breathe helps to burn the fuel and what is not consumed immediately, is stored in the liver approxGlycogen(a form of carbohydrate) or as fat. When there is no more room in the liver, the excess is stored elsewhere in the body in fat cells. Furthermore, metabolism creates carbon dioxide that we exhale and other waste materials that are excreted in the urine and feces. The process is done at different levels of efficiency in different people and under different circumstances in the same person.

For a long time, the best way to measure subjects' energy utilization was to house them for two weeks in a purpose-built laboratory, like ours, where researchers could measure everything they ate and track their weight. Another way was to put volunteers in a sealed room (called a calorimeter) and measure the amount of oxygen they breathe and the amount of carbon dioxide they emit. From these measurements we can estimate what the body's basic energy requirements are. Neither of these two methods is particularly convenient and does not adequately mimic the conditions of everyday life.

A much easier approach is to useDouble marking water, which contain tiny amounts of deuterium (²H) and oxygen 18 (¹⁸O), both are heavy and harmless non-radioactive isotopes. About one to two weeks after a person drinks twice the amount of water, the deuterium and some of the oxygen 18 are excreted in the urine. (The rest of the heavy oxygen is emitted by exhaling carbon dioxide.) Researchers take urine samples and compare the rate at which these two isotopes disappear from the body during this time. With this data, they can calculate the number of calories each subject consumes without interrupting their daily routine.

The method was developed in the 50s but for decades the double-marked water was too expensive for humans to drink. In the 80s, their price dropped and the measurement method became more efficient, although there were times when our lab had to spend almost $2,000 for one test. As a result, it took about 20 years to accumulate enough data to determine the amount of energy the body needs to prevent weight gain or loss.

These experiments, conducted by our group and conducted by other groups, helped us determine that humans do not need many calories to stay healthy and active. Any excess consumption quickly translates into weight gain. In this respect we are just like other primates, including chimpanzees and orangutans. An adult male of normal weight and typical height living in the USA today needs about 2,500 calories a day to maintain his weight and an average adult woman of normal weight needs about 2,000 calories a day. (Men tend to consume more because, on average, their bodies are larger and more muscular.)

In contrast, studies show that other biological species, such as red deer (The female tested in one of the experiments was six years old and weighed 100 kg) and gray seals (three adult females were tested in the experiment whose average weight was 120 kg) require two to three times more calories, compared to primates, in a kilogram-to-kilogram body weight calculation, to maintain their size.

It is tempting to assume that the energy needs of Americans are low because their lifestyle is mainly sedentary, but researchers have documented similar caloric needs in native populations who lead a very active lifestyle. Herman Ponzer from Hunter College and colleagues Measure the caloric intake of hunter-gatherers fromHadza tribe in northern Tanzania and found that the men needed an average of 2,649 calories per day. The women, who, like the men, tended to be smaller than their counterparts in other regions, needed only 1,877 calories. In another study of natives, Yakut people From Siberia, the men consumed 3,103 calories per day and the women 2,299 calories. It was also found that the men are Bni Aymara, natives living in the high altitudes of the Andes in South America, consume 2,653 calories a day and the women 2,342 calories.

Although our caloric requirements have not changed, government data show that Americans now consume an average of 500 more calories each day (the equivalent of a grilled chicken sandwich or two tacos at a fast food restaurant) than they did in the 70s. A small excess of calories, no more than 50 to 100 calories a day, the equivalent of a small cookie or two, can cause a one to three pound increase in body weight per year. This is how you easily reach an increase of 30-10 kg ten years later. Is it any wonder then that so many of us have become fat or even obese?

complex calories

The formula for maintaining a stable weight, meaning not consuming more calories than the body needs for heating, basic operations and physical activity, is just another way of saying that the first law of thermodynamics also applies to biological systems: the total amount of energy entering a closed system (in this case, the body) must be equal to the general quantity that comes out of it or accumulates in it. But the law does not require the body to use all food sources with the same efficiency. And here the question arises: "Do all calories contribute to weight gain to the same extent?"

Research in this field is developing and understanding why it took so long to get decisive answers requires a historical journey back to the late 90s to the village of Stour in Connecticut. There he built a chemist named Wilbur O. AtwaterThe first research station in the US designed to study food production and consumption. In fact Atwater was the first to prove that the first law of thermodynamics also applies to humans and animals. (Some contemporary scientists then believed that humans could be the exception to the rule.)

The experimental program of Metabolism Laboratories has changed but little since Atwater's day. To determine how much energy the body can produce from the three nutrients, proteins, fats and carbohydrates, he asked several male volunteers, each in turn, to stay in the calorimeter for several days. In the meantime, Atwater and his colleagues measured everything that the human guinea pig ate, and everything that was created from the food. Starting with the carbon dioxide that the volunteer exhaled and ending with the amounts of nitrogen, carbohydrates and other components in the urine and feces. Finally, the researchers determined that the body can produce about four calories of energy from a gram of proteins or carbohydrates and nine calories from a gram of fats. (These numbers are known today asAtwater Factors.)

It is understood that food does not come to us as pure protein, carbohydrate or fat. Salmon contains protein and fat. Apples contain carbohydrates and fiber. Milk contains fat, protein, carbohydrates and a lot of water. It turned out that the physiological properties and composition of food play a much more important role than the researchers expected in the digestion of food and the way the body absorbs calories.

In 2012, for example, he proved David Barr From the Beltsville Center for Human Nutrition Research of the US Department of Agriculture in Maryland, that the body cannot produce all the calories written on the nutrition label from some types of grains, depending on the process they have gone through. Whole fresh almonds, for example, are more difficult to digest than Atwater predicted, and we get about a third less calories from them, while we can metabolize all the calories from almond butter.

The digestion of whole grains, oats (quaker) and high-fiber breakfast cereals is also less efficient than we used to think. A new study conducted by our team looked at what happened when volunteers consumed a whole grain diet that included 30 grams of fiber, compared to a more typical American diet that contained half the amount of fiber. We discovered an increase in the number of calories lost in the feces and detected a jump in the metabolic rate. Combined, these changes add up to a net difference of 100 calories per day, a difference that can have a noticeable effect on weight over a period of years.

And so we and others have proven that not all calories are equal, at least when it comes to high-fiber grains and cereals. As scientists learn more about the difference in the efficiency of digestion of foods and how they affect the body's metabolic rate, it is likely that we will see several more such examples of differences large enough to affect how successful or difficult some people will be at maintaining their weight.

Energy expenditure

"Energy Equation": See an illustration on the American Scientific Israel website

So much for what we put in our mouths. What our body does with the food we eat moves us to the other side of the energy balance equation: energy expenditure. Researchers find a surprising amount of differences here as well.

One of the most common pieces of advice people who want to lose weight receive is to increase their physical training. Physical activity does help to keep the brain, bones and other body parts in proper condition. But detailed measurements conducted in our laboratory and by others show that physical activity is only responsible for about a third of energy expenditure (assuming body weight is stable). The body's basal metabolism, that is, the energy needed to maintain the body in a resting state, accounts for the other two thirds. It is interesting that the parts of the body that require the most energy are the brain and some internal organs, such as the heart and kidneys and not the skeletal muscles, although strength training may speed up the metabolism to some extent.

Moreover, anyone who has reached middle age understands very well that metabolism changes over time. Older people need fewer calories to maintain body function than they did when they were young. The metabolic rate is also different among different people. A study published in 1986 measured the metabolic rate of 130 people from 54 families. After taking into account the changes in age, gender and body composition, the researchers reported differences between the families of about 500 calories per day. The inescapable conclusion: when it comes to metabolic rate and your ability to lose weight or keep it off, genetics also play a role.

But let's assume you've already started losing weight. Naturally, your metabolic rate and energy requirements will decrease as your body gets smaller, and weight loss will slow. It's all a matter of physics: the first law of thermodynamics still applies to you. But the human body also obeys the evolutionary pressure that favors those who can persist in storing energy by becoming even more efficient at utilizing fuel. Indeed, studies show that the metabolic rate drops even more than expected during periods of weight loss. Then, when a person's body weight stabilizes at their new lower weight, exercise can help maintain it by compensating for the smaller body's decreased energy consumption.

Starving minds

But differences in Atwater factors and metabolic rate are not the end of the story. More and more studies prove that the brain plays a central role in coordinating signals received from a wide variety of physiological sensors in the body that alert the presence of food. The brain then creates a sensation of hunger and temptation to ensure we eat.

In other words, the role of hunger has always been to keep us alive, so there is no point in fighting it directly. Instead, one of the keys to success in maintaining weight is first of all to avoid situations of hunger and temptation in advance.

Single-meal feeding experiments conducted in several laboratories, including ours, show that meals rich in protein or fiber, or those that do not cause a sudden increase in blood sugar (glucose), are usually more satisfying and manage to suppress hunger better. (Carbohydrates are the most common source of blood glucose, but proteins can also produce it.) In summary, Roberts, one of us, published in 2000 stating that the consumption of calories in the hours after breakfast has Glycemic value high (such as highly processed breakfast cereals) was 29% higher compared to a breakfast with a low glycemic value (whole wheat, or a scrambled egg).

In fact, our team recently obtained preliminary data showing that hunger can be reduced during weight loss by choosing the right foods. Before dividing 133 volunteers into two groups, we asked them to answer a detailed questionnaire regarding the frequency with which they are hungry and the location and intensity of the feeling of hunger. Then we randomly assigned the volunteers to one of two programs: a weight loss program that emphasized foods rich in protein and fiber and with a low glycemic value (fish, legumes, apples, vegetables, grilled chicken and peeled wheat kernels, for example) or to a "waiting list" used by a group Review.

We clearly found that during six months, the members of the experimental group reported lower levels of hunger than the values ​​measured before the start of the experiment. At the end of the study, they also lost an average of eight kilograms, compared to the control group which added 0.9 kilograms.

Equally interesting, the experimental group also experienced fewer moments of craving for food, which means that the perception of pleasure in the brain changed. We then scanned the brains of 15 volunteers as they looked at pictures of a large variety of food items. The results showed that in the experimental group, the pleasure center of the brain became more active over time in response to images of grilled chicken, whole wheat sandwiches and high-fiber cereals. And at the same time their brains reacted less to images of French fries, fried chicken, chocolate candies and other fattening foods.

Personalized nutrition

The differences in the effect different foods have on reducing the feeling of hunger, the efficiency with which they are absorbed and the true, albeit limited, ability of our metabolism to adapt to changes in energy intake make weight maintenance a complex system. We keep finding special circumstances that affect different people differently. For example, it has been established that most obese people secrete relatively high levels of insulin, the hormone that helps the body process glucose. This phenomenon, the machine insulin resistance, leads to a great many health problems related to metabolism, such as an increased risk of heart attacks or the development of type 2 diabetes. When we treated such people for six months on a weight loss program based on foods with a low glycemic value, that is, more protein and fiber and less carbohydrates, we found that they lost weight More than what would have been taken from him was treated with a diet rich in carbohydrates with a high glycemic value.

Today, we regularly help research volunteers lose weight and keep it off. Despite the fact that the study described here with the 133 volunteers lasted six months and required participants to attend weekly meetings and answer e-mail during most of the time, only 11% of the volunteers dropped out. Some of the rest even cried at the last meeting with the team because they didn't want to say goodbye. Not only did they lose weight, but they succeeded above and beyond their expectations and felt that they had undergone both a psychological and physical change. And in the words of one of the participants: "The science worked."