Fasting: a guide to a practice that’s becoming increasingly popular

What the latest research shows, what doctors think, what people who practice fasting say

In 2016, Japanese biologist Yoshinori Ohsumi won the Nobel Prize for explaining the mechanism of autophagy. It went far beyond the scientific community.

Autophagy (Greek for “self-eating”) is the natural process of removing non-functional cellular components during times of stress. According to Professor Ohsumi’s observations, this phenomenon occurs when the body is starving – at least of yeast and mice. Researchers were able to identify the genes responsible for autophagy in the lab. The importance of this process was proven by an experiment with mice: those deprived of these genes died shortly after birth.

During autophagy, the cell gets rid of viruses, is able to fight harmful substances, and counteracts aging. So fasting prolongs your life? As of now, this is only a hypothesis, and it needs many years of research with a large number of participants to be tested. While many doctors view this practice negatively, describing it as too radical, there has been research that demonstrates the health benefits of intermittent fasting. Advocates of this method continue to tout the benefits it provides: weight loss, cholesterol reduction, reduced insulin resistance, and mental clarity, vigor, and creativity.

Fasting and its effects on the body

Hunger and satiety are controlled by the hypothalamus (a small area in the diencephalon) – within it, among its nuclei, is the ventrolateral hypothalamic nucleus (which controls hunger). The primary purpose of a hunger center is to ensure that a person is full. The stomach and intestines, as well as blood substances, provide the hunger center with this information. When the glucose concentration drops to a certain level, the neurons in the hunger center fire and begin to act. Adrenaline, for example, is released from the adrenal medulla, causing the breakdown of glycogen to increase blood glucose levels. This polysaccharide is also known as a “reserve carbohydrate” – during starvation, it helps the brain function properly.

Glucogen deposits mainly in the liver and muscles, and to a lesser extent in the kidneys and some brain cells. A person’s glycogen supply lasts for about 1-2 days, although with a great deal of physical activity, glycogen runs out faster. Hypoglycemia can theoretically cause a coma, but usually the body senses this in advance and begins to biosynthesise glucose – it starts the process of gluconeogenesis.

It occurs primarily in the liver and kidneys, which use glycerol (from adipose tissue) and amino acids from muscle tissue as raw materials during fasting. This process utilizes everything that can be used as a source of energy. Calories are generated from fat reserves.

As well, hormonal changes begin during this phase of fasting: insulin levels and thyroid hormone triiodothyronine (T3) drop, while glucagon levels rise (this hormone, by stimulating glycogen breakdown, helps to normalize blood glucose levels).

The behavior of leptin and ghrelin is changing – these hormones inform the brain about energy reserves. Blood leptin levels are related to fat storage. By penetrating the hypothalamus, it suppresses appetite. Under normal conditions, it is leptin – it is no coincidence that it is sometimes called the “satiety hormone” – that signals to a person that energy reserves are replenished and it is time to stop eating. It is logical that after a fast begins, its level declines.

On the other hand, ghrelin is called the “hunger hormone”. The cells of the stomach and small intestine secrete this hormone, which has a variety of effects on human homeostasis: it stimulates the release of growth hormone, alters carbohydrate and lipid metabolism, and stimulates the intake of food. Ghrelin gene expression is increased during periods of negative energy balance (during starvation).

The ghrelin level rises just before a meal and drops rapidly afterward. The serum level of the hormone has been found to rise significantly with caloric restriction, and later – with fasting. It only increases hunger.

After fasting for 12-14 hours, the number of ketone bodies in the body increases as well, although it then stabilizes at a level that is not harmful. The brain uses these as a primary source of energy for the central nervous system, gradually reducing the need for glucose and, consequently, gluconeogenic activity.

Ketone bodies are a by-product of ketosis (a metabolic state during which the body breaks down fats, releases fatty acids, and synthesizes ketone bodies). This is not to be confused with ketoacytosis, a pathological condition in which acidification of the body can result in death.

Early in biochemistry, glucose was regarded as a “cleaner” and more efficient fuel for the brain. Nowadays, ketones are preferred due to their higher energy density. The burning of glucose produces massive amounts of free radicals that damage the mitochondria (“our cellular powerhouses,” to quote psychiatrist Emily Deans) as well as the cells themselves.

As “superfuels,” ketones are said to be more efficient for the muscles and brain, providing 29% more energy than carbohydrates, proteins, and fats. As a result of ketones, many people have reported feeling a surge of energy and exceptional clarity of mind.

What are the effects of ketones on the body? As of now, there is no reliable scientific evidence that ketosis can positively affect brain function in healthy individuals.

We owe all the unpleasant effects of fasting to ketones: weakness, aches, palpitations, nausea, headaches, and bad breath. You should also keep in mind that the level of ketones in the body increases not only with a keto diet and targeted fasting, but when a person abuses alcohol or does not maintain good control of their diabetes.

What do the fasting advocates say?

A great number of mechanisms are launched in the body during fasting, according to Alexander Barvinsky, a therapist, specialist in unloading and dietary therapy at the SpaGolod clinic. According to his calculations, an average person with a normal weight carries around 120,000 kcal in fat reserves (women carry more, men less). It is a very rough estimate. Fat normally makes up 20–25% of the average human body weight (70–80 kg), and a kilogram of fat contains about 9000 kcal.

“It is the presence of these resources that demonstrates that nature has adapted us, Homo sapiens, to starvation. When famine strikes, we are able to use all these reserves to the end,” the doctor says.

Angus Barbieri, who at 27 weighed 207 kg, is a well-known example. In order to lose weight, he decided to fast under the supervision of his doctor. At first, they had no intention of “prolonging” the fasting period, but the patient adapted well and expressed a desire to continue. The physician allowed him to take multivitamin supplements, vitamin C, and non-caloric drinks for 382 days. He weighed 81.6 kg at the end of his fast. He gained only 7 kg over the next five years. Doctors have not found any negative effects from fasting. Barbieri died at the age of 51.

However, Barbieri’s situation is unique. The Guinness Book of Records has since stopped recording such experiences as they are life-threatening. Most people prefer a less drastic way – intermittent fasting (IF). There is some evidence that it may have some health benefits.

For instance, it can increase insulin sensitivity, increase BDNF (brain protein hormone), which promotes the growth of new nerve cells, and prevent type 2 diabetes and neurodegenerative diseases (Alzheimer’s and Parkinson’s). Further, intermittent fasting practitioners claim that it boosts energy, improves memory, and improves brain function.

In Silicon Valley, the practice seems to be popular due to its feeling of clarity and energy. Between 6:30 pm and 9:00 pm, Twitter founder Jack Dorsey eats one meal a day. It’s usually fish, chicken, or steak with lettuce, spinach, or Brussels sprouts. He likes berries and dark chocolate for dessert, and he sometimes allows himself a glass of red wine. His first two weeks in this mode were challenging, but then he noticed changes: “I feel more focused during the day.” Also, he said he fell asleep faster and slept better in general.

Former Evernote CEO Phil Libin also practices intermittent fasting. He admitted that he felt “mildly euphoric and constantly energized, and his mood and focus were greatly improved.” The beginning of the fast was quite frightening: “On the first day of fasting, I thought I was going to die. It was even worse on the second day. I felt better on the third day than I had in twenty years,” he recalls. The bonus to this state is a feeling of bliss at every meal: “No more boring dinners!”

David Sinclair, an Australian aging scientist, believes fasting prolongs youth. He says he fasts intermittently as often as he can. He usually abstains from food 16 hours a day. For him, sticking to a schedule is easier than cutting calories.

Also in the starving club are Daniel Gross of Y Combinator, Pavel Durov and many biohackers. Kevin Rose, a Digg founder, launched the Zero smartphone app to help intermittent fasting practitioners track the amount of time they go without food.

Various types of fasting

Intermittent fasting

Intermittent fasting has several types.

5:2. Five days a week, you eat as usual, but the remaining two days, you severely reduce your daily calorie intake. Recommendations are: 500 kcal for women and 600 kcal for men. In an experiment conducted by American nutritionists, 100 volunteers aged 35 to 65 lost more weight than a control group that did not change their diet. Interesting enough, even a year after the experiment, the people did not gain weight.

Researchers have found that the 5:2 diet is equally effective to a diet that reduces daily calories by 20%. Yet there are indications that the 5:2 diet is still preferable long-term: the diet lowers blood glucose and cholesterol levels, as well as lipids, reducing the chances of atherosclerosis and coronary heart disease.

16/8 and 14/10. The common factor is that meals fit into one “window”. The first case describes a day divided into 16 hours and 8 hours. There is an 8-hour interval for eating (for example, from 8 to 16 or from 9 to 17), and then only drinking is allowed afterward (within 16 hours).

The second intermittent fasting option is considered one of the most sparing: the 10-hour “window” for eating, the 14-hour “window” for hunger.

“The window” can be adjusted to your rhythm of life: there are six-hour and fourteen-hour versions. There is evidence that the 18/6 schedule (with a 6-hour window for eating) improves insulin sensitivity, appetite, and blood pressure. One study examined 420 volunteers for five weeks and found that those who ate full (the most energy-rich meal of the day) lost less weight than those who followed a regimen.

24/0. The most radical method is to fast between meals for a day. It is advised to follow it with extreme caution. Over time, the positive effects of fasting fade, as the body adapts to it.

Randomized controlled trials show that those who adhere to such a regime are more likely to refuse it than those who do not restrict themselves in food so drastically. The performance of this method is comparable to that of a 20-25% calorie restriction.

36/12. Fast every other day. The most rigorous intermittent fasting ever: 36 hours of fasting followed by a 12-hour window for eating.

What is the best fasting mode?

The one that a person can stick with for the longest period of time.

According to a recent study, the most effective and safest option for people with a normal body mass index (BMI) is 36/12. By doing so, the calorie content of the diet could be reduced by almost three times, while those who participated in the study had no dietary restrictions during the 12-hour period.

Their health indicators have improved: they have lost up to 3.5 kilos of excess weight in one month, have reduced the level of visceral fat (while maintaining muscle mass – this is very important for athletes), their level of total cholesterol has decreased, their level of ketone bodies has increased, and so on. The side effects did not appear for at least six months after the studies.

The system is hard to follow, but might be effective as a weight loss strategy in the 8-12 week range. For most people, narrowing the eating window will be easier because it doesn’t involve counting calories.

Dark side of fasting

Various doctors and researchers have also reported adverse effects of intermittent fasting. For instance, it can:

• Disrupt sleep (decreases the length of REM sleep);
• Diabetes and other serious diseases can occur from injuries to the pancreas and reduced insulin sensitivity;
• Concentration issues may arise. A person feels focused at first, they may interpret this state as productive, but in fact, their brain is signaling their body that they are starving, explains Jennifer Gaudiani, MD, PhD. Alyssa Ramsey, a nutritionist in New York, says that intermittent fasting will lead to a decrease in concentration in the long run;
• Increasing cortisol level (stress hormone) can negate the benefits of fasting, according to Ramsey. In addition, high cortisol levels are associated with fat storage, which is not good for losing weight;
• Hair loss and irregular periods can result.

According to nutritionists, fasting is contraindicated for children, diabetics, pregnant women (and women planning to conceive in the near future), and breastfeeding mothers.

According to nutritionist Farzanna Nasser, people with adrenal problems should also not fast, since doing so can only make symptoms worse. A person with chronic stress has already overproduced cortisol, so fasting is definitely not the best choice.

Eating disorders may be masked by intermittent fasting. But not just to mask. Evelyn Tribol, a nutritionist and author of Intuitive Eating, believes intermittent fasting puts one at risk of eating disorders such as bulimia.

It is not necessary for all intermittent fasters to develop an eating disorder. According to professor of psychiatry Christina Vierenga of the University of California at San Diego, if a person is genetically predisposed to these disorders, fasting can trigger them.

Furthermore, not everyone achieves the clarity of mind that starving people talk about. According to Fast Company, writer, screenwriter, and journalist Michael Grothaus reported no significant improvement in his own productivity after several cycles of a two-day fast. Nutritionists strongly advised Grothaus not to starve: an extreme lack of energy can lead to hormonal imbalances and an overly emotional relationship with food.

Fasting is it good or bad? Barvinsky believes it is impossible to give an unambiguous answer to this question. Fasting can be both harmful and beneficial. It all depends on how you approach it.

An action plan

1. Avoid fasting. Doctors generally believe that fasting is dangerous. An unexpected failure can happen at any point in the process. Hunger is a stressor, and stress is thought to be a cause of a huge number of diseases.

2. If you still decide to do it, see a doctor. Find out if you have any contraindications before undertaking a risky experiment. An examination of the whole body is performed in a fasting clinic, which begins with a clinical blood test. This can help determine conditions that a person is not yet aware of. In addition, it is very important to check the adrenal glands – using an ultrasound and a cortisol test.

It is paradoxical that the indications and contraindications of fasting can be the same (which is why consultation with a medical professional is essential). There is evidence to support that this process can help fight type 2 diabetes, yet simultaneously aggravate it, therefore, in the classic panel of analyses for those who wish to try fasting, the following items are included:

• The total cholesterol level;
• The triglycerides level;
• the LDL cholesterol level;
• HDL cholesterol level;
• Glucose levels;
• IGF-1 (insulin-like growth factor);
• C-reactive protein (inflammation marker).

3. Ensure you’re mentally prepared. Even though stress can be good or bad, it is important to make mindful fasting a good thing. If you are currently mentally unstable or all your time and energy is being consumed by some important project, postpone your fast.

4. Select the appropriate method. There is no consensus among scientists on the best way to fast. As with any diet, you need to be consistent when fasting – you can do some research on your own and decide what you prefer.

To lose weight. There is evidence that the 36/12 option is effective for weight loss in people with normal body masses. Although this path is quite difficult to follow, perhaps it is a good idea to start with the softest – 14/10.

The prevention of heart disease. Long-term, option 5/2 lowers blood glucose levels and cholesterol levels and reduces lipids.

The prevention of diabetes. Research shows that the 18/6 schedule (with a 6-hour “window” for eating) improves insulin sensitivity, appetite, and blood pressure.

For a special feeling. People who fast for several days report extraordinary energy and a special attitude (see Akulina Mezinova and Phil Libin’s comments above).

5. Keep track of biological indicators. After changing the diet, consult your doctor and take the tests (see point 2).