The questions that immediately arise are: how little do you need to eat? How does it work? And most importantly, what do you do if you still want to eat?
Overeating is really not a good idea, it's true. When someone in our mind “eats a lot”, they get more energy than they expend. At the same time, the excess energy is stored in the form of fat. Obesity, in turn, brings with it a "friendly company" of related diseases. But that's not what we're talking about now. Back in 1935 it was discovered that animals that eat less than they expend energy, live longer than their relatives who keep the balance. Since then, many organisms, from yeast and worms to mice and monkeys, have been able to extend their lives in this simple way.
But what about humans?
Unlike a worm or a mouse, it is difficult to set up a controlled experiment with humans that lasts a lifetime. Therefore, we do not yet have scientifically reliable results. But the events of the 20th century have provided us with data that no one ordered. Such random experiments were, for example, the world wars. The population of some countries did not suffer serious losses during the fighting, but at the same time experienced a shortage of food. During the First World War, for example, the residents of Copenhagen were forced to eat less than usual for two years because of the cessation of trade with the United States and Britain. Afterward, the government's food advisor estimated that the death rate in the capital of the Danish kingdom dropped by 34%.
During World War II, the residents of occupied Norway were restricted in their eating, and the number of deaths caused by circulatory diseases dropped by 30% compared to pre-war times - according to Norwegian researchers, largely due to the forced diet.
A third unforeseen experiment unfolded in Japan. Back in the late twentieth century, the number of long-livers in Okinawa was 4-5 times higher than in other civilized countries. The mortality rate of the elderly was lower and the average life expectancy was higher, not only compared to other countries, but also compared to other Japanese islands. It turned out that a typical Okinawan diet (lots of fruits and vegetables, fish, soy, rice) contained fewer calories than the diets of other regions of Japan, not to mention the United States . However, in the 1960s, American soldiers brought the fast food culture with them, and it penetrated Okinawa. As a result, at the beginning of the 21st century, those born in Okinawa can no longer expect to live as long as others.
How much is too little to eat?
The main thing is not to confuse calorie restriction with starvation and malnutrition. First, a person should not starve. Scientists talk about reducing the caloric content of the diet by an average of 20-30%. That is, a person in this case consumes 20-30% less energy than he or she expends. A logical question arises: why then a person does not run out at all? Below we will tell you how, with a nutritional deficit, the body begins to spend resources more efficiently. Secondly, it is necessary that the diet includes all the necessary groups of substances: proteins, fats, carbohydrates, vitamins, etc. This can be clearly seen in the above examples. Why did scientists draw from the stories of the inhabitants of Scandinavia during the world wars? Because although they experienced dietary restrictions, their diet was still nutritious. They were able to eat fresh vegetables and fish, for example. It's the same story with the people of Okinawa.
In fact, planned experiments with humans were also conducted. For example, the CALERIE (Comprehensive Assessment of Long-term Effects of Reducing Energy Intake) project tried volunteers for several months to eat 25% fewer calories and exercise occasionally. The studies are recent, so mortality data won't be available for a while. But already at the end of the first experiments it became clear that those who ate less, compared to the control group decreased the likelihood of cardiovascular disease and diabetes: the concentration of relevant substances in the blood decreased markers.
More severe restrictions were also studied: in the project Minnesota starvation experiment people consumed 40% less than necessary (on average per day received 1800 kcal, and spent 3000). In this case, the researchers were trying to recreate the situation of starvation during the war. In addition to improving some metabolic indicators, the results, as you might expect, did not look particularly encouraging: weakness, edema, depression, behavioral disorders ... However, after returning to a normal diet, these symptoms disappeared. But it is interesting that about 50% of the experiment participants, having reached the age of 80, lived eight years longer than expected for their generation.
How do I know how much energy I'm expending?
Unless you're participating in an experiment, there's no way to measure the energy expenditure of your lifestyle on your own. There are several techniques in the laboratory, most of which boil down to measuring the amount of carbon dioxide a person produces. It is formed as a result of cell respiration, that is, the breakdown of nutrients with the release of energy. For example, you can put the subject in a sealed room and watch how the concentration of carbon dioxide will change there. However, to simulate daily activity, you would have to set up exercise machines and treadmills in the room.
To avoid building a room, you can use the double labeled water method. This is a water molecule made up of heavy isotopes of hydrogen and oxygen. We inject labeled water into the body, and after a while we measure the amount of isotopes in the blood. Over time, there will be fewer and fewer of them. At the same time, we know that hydrogen can leave the body mainly as part of water, and oxygen can also leave the body as part of carbon dioxide. So we count how much oxygen the body has lost and subtract the amount of hydrogen lost. We get the amount of carbon dioxide that the body exhaled, and it is already recalculated to the amount of energy expended.
In experiments with animals, scientists measure consumption ad libitum, that is, until satiety. We are not mice, and we are often forced to eat not by the need for energy, but by many other factors: habits, socialization, depression, etc. Nevertheless, you can track how much food you need - in calories, of course - to stop feeling hungry. You can then subtract 20-25% from this value. This will give you the number of calories you need to get daily if you decide to get into the skin of an Okinawan long-lived man.
What kind of food should we eat?
The cells in our body can digest any biopolymers, but at different efficiencies and rates. The most common food is glucose. The complete chain of its breakdown includes an anaerobic step in the cytoplasm (glycolysis) and processes involving oxygen in the mitochondria (Krebs cycle and oxidative phosphorylation). It is possible to stop immediately after glycolysis. This will be less favorable in terms of energy, but will take less time. If you go all the way to the end, however, you get more energy, but not right away. With other food options, you cannot “speed up”: amino acids and fatty acids are first converted into an intermediate product, acetyl-CoA, which is involved in mitochondrial processes of energy extraction. That is, the breakdown of amino acids and fatty acids always occurs aerobically, with the participation of oxygen
Cells can regulate the type of their energy metabolism by changing the glycolysis/ aerobic respiration ratio. By feeding them glucose, we offer them a simpler and less efficient way to obtain energy. Therefore, if we want to limit calories, we need to force the cells to utilize all available energy and therefore reduce carbohydrates. In a radical version, this leads to the ketogenic diet, where there are very few carbohydrates, but a lot of fat. The benefits of this diet are still difficult to assess. It has long been used to treat epilepsy, and in the prevention of neurodegenerative diseases, it has shown itself quite well. Nevertheless, it is quite difficult to sustain it, and there are no data on life expectancy on it yet. So, the main thing is to reduce the amount of carbohydrates, but at the same time do not allow radical distortions such as the complete exclusion of carbohydrates from the diet.
How often should I eat?
Calorie restriction itself has nothing to do with the diet. At least, if we are talking about prolonging life, not about losing weight or improving the gastrointestinal tract. But interval fasting is often mentioned in connection with calorie restriction. The idea of the latter is that we restrict ourselves only at certain intervals - for example, one or two days a week. As a result, the same cellular mechanisms are activated as with long-term caloric restriction, but with a certain periodicity. Recent studies show that both methods are effective, but calorie restriction still prolongs the life of experimental animals more.
How does calorie restriction prolong life?
This seems to be the most difficult question, and a definitive answer is still being sought. Apparently, calorie restriction puts the cell on alert. Here's how it happens. When the cell is short of glucose, it has to use it via the “long” pathway. To do this, the mitochondria consume oxygen, which inevitably produces free radicals - molecules that are active in chemical reactions. The free radicals attack all surrounding molecules, and damage begins to accumulate in the cell. This is called oxidative stress. A cell's response to stress depends on the severity of the stress, that is, the number of radicals. If there are too many, the cell can prematurely age or commit suicide. A mild stress, on the contrary, can induce the cell to mobilize its resources - this effect is called hormesis.
To date, we know of three major “switch” proteins . These are mTOR kinase, insulin-like growth factor (IGF1) and growth hormone (somatotropin). They all work as food sensors, responding to the presence of nutrients themselves (glucose and other monomers) or their energy equivalents (e.g., ATP) in the cell. If food is present, mTOR triggers protein synthesis, growth hormone triggers cell growth, and IGF triggers the uptake of substances from outside the cell and their storage inside the cell. All these processes lead to the accumulation of free radicals and defective proteins in the cell - by-products of intensive metabolism. Calorie restriction reduces the activity of these three regulators and the corresponding signaling pathways. At the same time, the cell begins to produce its own antioxidants and starts autophagy - the process of partial digestion of its proteins and organelles. This allows the cell to get rid of accumulated damage and become more resistant to stresses
Are there any other benefits to eating little?
Sure. Oxidative stress affects more than just the rate of cellular aging. For example, it accompanies many neurodegenerative diseases. So calorie restriction can help prevent them. And even healthy people who eat less have improved verbal memory and stem cell division in the brain . In addition, lack of food increases the cells' sensitivity to insulin. Insulin stimulates the cells to grab sugar from the blood, and since sugar is scarce, the signal is to start grabbing more actively. This reduces the risk of developing type II diabetes, in which cells stop responding to insulin and blood sugar builds up. Finally, oxidative stress underlies inflammation, so calorie restriction dampens the immune response. Some studies have shown that short-term fasting before and after cavity surgeries improves outcomes and wound healing. Calorie restriction not only motivates normal cells to survive, but also hits tumor cells. Cancer cells change their metabolism and switch to the rapid breakdown of glucose. So when its concentration in the blood drops, so do the tumor's chances of survival.
What can I do if I can't eat less?
It's really not easy: even the organizers of the CALERIE project complain that their volunteers do not manage to limit themselves in eating properly. So the only advice here is to train your willpower or wait for more convincing evidence that calorie restriction works. But if it happens that you are not allowed to eat less for medical reasons, you can still look for a way out. There are several medicinal analogs to fasting, but - beware! - none of them are yet recommended for use without sufficient indications. In other words, losing weight and prolonging life with pills alone does not seem to work.
An effect similar to calorie restriction is given by the drug rapamycin. This is a very multifunctional substance: initially it was discovered as an antibiotic, then it was found to have immunosuppressive properties (and it is still used to prevent rejection of transplants), and also found that it inhibits tumor growth by blocking mTOR (and now its “relatives” - temsirolimus and everolimus - are approved in the U.S. for cancer treatment). And finally it turned out that rapamycin prolongs the life of mice. Actually, thanks to it, the mTOR protein was discovered, the name of which stands for mammalian target of rapamycin in mammals. Generally, rapamycin has some rather unpleasant side effects (e.g., immune suppression). But in low concentrations, it may be less dangerous. Just recently, the first clinical trials of rapamycin analogs ended, which increased the resistance of elderly people to seasonal colds and helped them respond more effectively to vaccinations. So now we know that this treatment is at least safe, and we can wait for new clinical trials.
There are other analogs to calorie restriction. For example, metformin is a drug that helps you lose weight in type II diabetes. It may work as an analog of fasting, but it is still unknown how effective it is in healthy people without diabetes. And it has so far only reliably extended life in mice. The only drug that can be taken without serious indications is resveratrol. But the effectiveness of this dietary supplement has not yet been confirmed by clinical trials.
So what's the bottom line? Apparently, consuming fewer calories is really useful if you do not suffer from serious diseases. But you can't do it with pills, so you'll have to exert your willpower. Or sign up as a volunteer for a clinical trial - where you will definitely be closely followed