Interval Diet: Contraindications And Side Effects

Victoria Aly Author: Victoria Aly Time for reading: ~14 minutes Last Updated: September 12, 2022
Interval Diet: Contraindications And Side Effects

Intermittent fasting is a diet that involves alternating meals and then restricting them for a certain period of time.


Intermittent fasting is a diet that involves alternating meals and then restricting them for a certain period of time.

Weight loss, correction of metabolic disorders, and even a component of oncology therapy - is it really such an effective tool in the hands of a nutritionist, as fashion magazines and foreign blogs assure?

Are there any restrictions and contraindications? Let's figure out if this trend is new in the world of health and medicine, or just a long-forgotten old one.

Intermittent fasting: rules and techniques

So, as mentioned earlier, intermittent fasting involves alternating periods of hunger and a clear time frame during which you can eat food.

The simplest option is the 10/14 system, which assumes that for ten hours a person eats, and the remaining fourteen (including the time allotted for sleep) abstain from eating. In other words, if dinner was at eight in the evening, then breakfast should be no earlier than at 6 in the morning. Nothing complicated, agree.

After the adaptation of the body, you can switch to more effective methods: 14/10, 16/8, 20/4 - the latter, it must be said, remains the subject of a scientific dispute and, as we will demonstrate below, is far from being shown to everyone.

In general, any of the intermittent fasting regimes implies the complete exclusion of snacks - and, to be honest, it’s hard to fit second breakfast and afternoon snack, as an addition to the main meals, within the same eight hours. Do not forget that a 5-time diet, even taking into account the subsequent abstinence from food, creates a considerable burden on the pancreas. It's all about insulin - a hormone of protein nature, which is invariably released in response to any incoming product.


Of course, its primary role is to control the level of sugar or, in the language of biochemistry, glucose in the blood serum. This indicator is strictly regulated and any deviation (both up and down) entails a number of negative consequences. So, with an increase in the concentration of glucose in the blood (which naturally occurs due to the absorption of carbohydrates previously split by enzyme complexes in the small intestine), insulin helps to reduce it, providing entry into the cells.

Glucose, devoid of fat solubility by nature, cannot independently overcome a selectively permeable barrier - such a passport control at the border of cellular and extracellular environments. She needs a special transporter - a protein carrier that would help her get inside, that is, into the cytoplasm and join in the future in the path of energy production. This is GLUT4, an insulin-dependent protein that performs its functions in adipose tissue and muscle (including the myocardium).


However, the more often we eat food, the longer insulin circulates in the blood: its half-life does not depend on the components of the incoming food and is about 40 minutes. The constant presence of this hormone in the serum reduces the sensitivity of receptors to it - and over time they stop responding to its signals, which makes it impossible for glucose to enter the cells, mediating its presence in the systemic circulation. This is perhaps the key step in the pathogenesis of type 2 diabetes mellitus.

What happens to the body during fasting

In humans, as in most mammals, the reserve reserves of carbohydrates are concentrated in the liver in the form of glycogen. On average, they are enough to maintain the energy needs of the body for 12-24 hours - everything, again, depends on the degree of physical activity and the functional load on organs and systems.

After the depletion of sugar reserves, the metabolism switches: here, in hepatocytes, a factory for the production of ketone bodies is launched. The substrate for the formation of the latter are fatty acids, which are released under the action of stress hormones (functional insulin antagonists) from adipocytes of adipose tissue, as well as some amino acids.

In addition, the process of gluconeogenesis is activated: liver cells independently begin to reproduce glucose from various non-carbohydrate components - in particular, from the structural building blocks of proteins undergoing breakdown. All these processes contribute to the maintenance of life for about a month - of course, much will be determined by age, gender, initial weight and general condition of the body. However, for example, in penguins, such compensatory mechanisms allow them to survive for more than five months - and this is in conditions of the absolute absence of any food!

Ketone bodies are also used as an energy source by brain neurons: due to the fact that fatty acids circulating in the blood only in the state associated with large protein molecules cannot overcome the border at the junction of blood vessels and nervous tissue - the blood-brain barrier.

Of interest are those adaptive responses that are observed during starvation in the CNS and are associated with brain-derived neurotrophic factor (BDNF). For example, studies in animal models have shown that restriction of food intake in combination with exercises on a running wheel in laboratory rats was associated with increased BDNF synthesis, which was accompanied by an increase in cell resistance to damaging factors and stimulation of neurogenesis.

Interestingly, one of the BDNF synthesis stimulators is just ketone bodies (beta-hydroxybutyrate), which not only serve as a purely raw material for energy generation processes, but also carry out a number of signal reactions.

Effects of intermittent fasting

Fasting has been practiced for centuries, if not millennia, but its beneficial effects are only now being discussed. \

I must say that it is characteristic not only of man, but also of most living organisms. So, for example, in rodents it minimizes the risks of developing diabetes, cancer, cardiovascular diseases, neurodegeneration, and in non-nuclear organisms, by changing metabolic pathways and susceptibility to stress, it helps to prolong life.

Obesity, hypertension, asthma and even autoimmune diseases (including, in particular, rheumatoid arthritis) - the list of pathologies that this diet effectively prevents is expanding every year.

Let's take a closer look at some of the effects intermittent fasting has on the human body:

  1. Prevention of neurodegenerative disorders:

    It is carried out mainly by suppressing the accumulation of damaged molecules (in particular, under the influence of free radicals), improving bioenergetics, as well as stimulating the formation of the previously mentioned neurotrophic factor in the brain, which regulates the mechanisms of development of nerve cells. There is also an increase in the level of antioxidants and inhibition of pro-inflammatory signaling molecules: interleukin-6 and tumor necrosis factor alpha.

    It is believed that this diet also has a beneficial effect on synapses, through which the transmission of impulses between two neurons is carried out.


    "Nutrition for a nursing mother: the impact on the child's body" More

    However, on the other hand, the ability of intermittent fasting to stimulate the progression of such a disease of the nervous system as amyotrophic sclerosis is not excluded: this is due, as scientists suggest, to the inability of the motor neurons localized in the spinal cord and which are the target for this pathology to adapt to moderate stress, what is caused by starvation.


  2. Prevention and treatment of metabolic syndrome - a complex disorder that includes insulin resistance (that is, a decrease in the sensitivity of cellular receptors to insulin) in combination with hypertension, obesity and lipid disorders.

    Intermittent fasting significantly reduced glycated hemoglobin levels in study volunteers, increasing the effectiveness of type 2 diabetes therapy. In addition, preclinical studies note other positive effects in patients with impaired carbohydrate metabolism, invariably accompanied by oxidative stress:

    • decreased serum glucose concentration;

    • various mechanisms of stress resistance were activated;

    • protection from free radicals, leading to damage, first of all, of membrane phospholipids, was carried out, and inflammation processes were suppressed.


  3. Slowing down the aging process associated with oxidative stress, hyperglycemia, accumulation of dysfunctional proteins and other macromolecules.

    For example, in asthmatic patients, markers of free radical damage decreased as early as 2 weeks after changing dietary patterns and switching to intermittent fasting, as did another group of volunteers, consisting of overweight women with a significant risk of breast cancer.


    An equally interesting study was conducted on rats deficient in estrogens, sex hormones that are involved not only in the regulation of many metabolic reactions, but also have a significant impact on the cognitive functions of the body. Their deficiency was associated with the deposition of an abnormal protein, amyloid, in nerve cells—in other words, neuroinflammation was noted. This, in turn, led to the development of pathologies similar to Alzheimer's disease and was accompanied, in particular, by memory loss.

    Interestingly, the introduction of amyloid into such laboratory animals directly into the hippocampus, one of the key structures of the brain, affected the transmission of insulin signals in this area of ​​the CNS and the progression of insulin resistance. However, the transition to intermittent fasting significantly improved the course of pathology in rats by suppressing the accumulation of abnormal proteins in neurons and inhibiting inflammatory reactions.


  4. Induction of mitochondrial biosynthesis - with intermittent fasting, there is an increased formation of small power plants in the structures of the brain.

    Study: Fasting: Molecular Mechanisms and Clinical Applications, Intermittent fasting protects against the deterioration of cognitive function, energy metabolism and dyslipidemia in Alzheimer's disease-induced estrogen deficient rats, Fasting as a Therapy in Neurological Disease


Autophagy: anti-cancer defense mechanisms

In 2016, the world was actively talking about autophagy - and all thanks to the Japanese scientist Yoshinori Ohsumi, who first discovered the mechanisms for its implementation, for which he was awarded the Nobel Prize.

Autophagy is an evolutionarily established process, which is a kind of “self-devouring”: with the help of special organelles - lysosomes - and the hydrolytic enzymes contained in them, intracellular structures are split: proteins of macromolecules damaged or changed under the action of viruses. The substances formed during their degradation: nucleotides, amino acids, fatty acids are used in other pathways of metabolism and life support.

Intermittent fasting has been associated with a significant increase in the effectiveness of chemotherapy and radiation treatment of tumors, in particular, this was noted in relation to breast cancer. It also reduced the likelihood of side effects arising from therapy (both gastrointestinal and general: weakness and fatigue) and reduced weight loss, which in some way can be considered the prevention of cachexia.

In addition, it promoted the activation of DNA repair, thereby preventing the development of mutations and, moreover, correlated with a decrease in insulin-like growth factor-1, a protein known for its anabolic effects.


So, autophagy is a normal, physiological process that protects the population of cells from the emergence of mutants. In addition, it can be enhanced under the influence of stress factors (oxygen starvation, damage to the genetic apparatus, malnutrition), when the risk of certain “mistakes” increases - especially at the molecular level.

The study of animal models has shown that this mechanism of protection against carcinogenesis is implemented primarily by suppressing oxidative stress and inflammation, preventing cell DNA damage and the accumulation of abnormal, dysfunctional ultrastructures in them. However, the reverse role of autophagy is not excluded: in particular, its influence on the progression of the tumor process.

For example, some scientists suggest that, by destroying the structural building blocks of defective organelles, autophagy thereby provides nutritional raw materials for cancer cells, maintaining their viability. It is natural that the rate of this process in atypical tissues is much higher than in normal ones.

Interestingly, new work has emerged pointing to the potential role of autophagy in the implementation of metastasis - that is, the emergence of secondary tumor foci.

Study: Autophagy and intermittent fasting: the connection for cancer therapy?

Contraindications for intermittent fasting

Intermittent fasting is contraindicated in exacerbations of inflammatory diseases of the mucosa of the gastrointestinal tract. Under the conditions of the irritating effect of hydrochloric acid on the stomach wall and the initial sections of the duodenum, it is necessary to provide favorable conditions for the regeneration processes to take place: taking gastroprotectors, antioxidants, and working with the folate cycle.

In addition, such a regimen will exacerbate the manifestations characteristic of adrenal exhaustion - especially its extreme degree. We have already said that with a decrease in blood glucose levels, insulin antagonist hormones are connected: first of all, glucagon produced by pancreatic cells, as well as cortisol and adrenaline, which produce the cortical and, accordingly, the adrenal medulla.

Constant stimulation of the production of stress hormones is fraught with menstrual irregularities in women: there is an effect of stealing from pregnenolone, the mother of all steroid hormones. Under the influence of this kind of unfavorable factors, it follows the path of formation of not sex hormones, but glucocorticoids.

Side effects of intermittent fasting

The first, and perhaps the most obvious, is cholestasis or bile stasis. This greenish-golden secret, produced by liver cells and accumulated with subsequent concentration in the gallbladder, is released in response to food intake (with the exception of carbohydrate), when a hormone such as cholecystokinin is secreted into the lumen of the initial sections of the intestine.

Stagnation of bile, as a rule, is also observed in patients who adhere to both three meals a day and fractional meals and often develops long before the onset of starvation. This is definitely one of the most common problems that nutritionists and doctors face in their practice.


In most cases, cholestasis is caused by an excess of carbohydrate food, which leads to excessive formation of fat (triglycerides) in hepatocytes and a violation of the blood lipid spectrum. It is the predominance of cholesterol over phospholipids and bile acids in the composition of this digestive secretion that disrupts the fluidity of the latter and predisposes to cholelithiasis.

Other causes of bile outflow disorders are:

  • helminthic invasion;

  • biliary dyskinesia;

  • syndrome of excessive bacterial growth in the small intestine, which is accompanied by excessive gas formation due to increased fermentation of organic compounds by overgrown colonies, which affects the form of increased pressure, which impedes the secretion of digestive juices.

If you have violations of the formation or outflow of bile, it is necessary, first of all, to deal with these pathologies. so as not to aggravate them. Below are some of the typical signs of cholestasis:

  • constipation - bile acts as a stimulant of intestinal motility;

  • discomfort in the right hypochondrium;

  • nausea and belching;

  • headache - especially along the perimeter of the temporal bones;

  • itching - due to the toxic effect of bile acids.

  • accumulation of copper in the body.


In general, in the absence of characteristic complaints and manifestations on ultrasound of the abdominal organs, to prevent the development of cholestasis, we recommend, especially when practicing intermittent fasting, taking bile stimulants and drugs that improve its composition and properties:

  1. Wormwood tincture.

  2. Dandelion root.

  3. Ursodeoxycholic acid.

  4. sunflower lecithin.

  5. Choline.

  6. Coffee.

  7. Ginger and turmeric.

In addition, hypoglycemia may develop - a decrease in the level of glucose in the serum below the optimal level for the functioning of all systems and organs, which the body persistently signals - first from the autonomic nervous system. Characteristic:

  • weakness;

  • blurred consciousness;

  • headache;

  • visual impairment;

  • increased sweating;

  • tremor.

Persons predisposed to hypoglycemia are not recommended fasting (especially long-term) - at least without medical supervision.

Since intermittent fasting implies a certain time frame during which food intake will be limited, you should focus on protein-fat foods in your diet - the latter, in particular, will provide you with satiety and for a long time discard any thoughts about food.

Carbohydrates, especially simple sugars, due to their structure, which ensures rapid absorption in the small intestine and, accordingly, a lightning-fast reaction from the pancreas, are only able to cover the energy costs of the body for a short period of time. In addition, one should take into account the fact that fructose, bypassing the insulin and leptin secretion pathways, does not cause the onset of satiety - this is why fruits should not be considered as an independent meal.


Below we have given an approximate diet that is guaranteed to provide you with energy for the whole day.

Breakfast options:
  1. Ghee and coconut milk omelet with cherry tomatoes and parmesan.

  2. Gluten-free toast with avocado, arugula and egg Benedict.

  3. Cheese quiche with fish and eggs on almond flour.

  4. Vegetable fritters with salted salmon.

  5. Cod liver with quinoa and green salad.

  6. Homemade yogurt with nut granola, almond chips and a handful of your favorite berries.

Lunch ideas:
  1. Baked salmon fillet with creamy sauce; grilled vegetables.

  2. Chicken broth with funchose and meatballs.

  3. Roll with falafel, homemade pesto, leafy vegetables and cherry tomatoes.

  4. Broccoli and salmon pie with nut flour.

  5. Baked cauliflower with turkey fillet and fresh vegetables.

Dinner options:
  1. Cauliflower risotto with mushrooms.

  2. Baked rabbit and amaranth as a side dish.

  3. Tilapia fillet and grilled vegetables.

  4. Chicken hearts with quinoa.

The material is based on research:
  • Fasting: Molecular Mechanisms and Clinical Applications

  • Intermittent fasting protects against the deterioration of cognitive function, energy metabolism and dyslipidemia in Alzheimer's disease-induced estrogen deficient rats

  • Fasting as a Therapy in Neurological Disease

  • Autophagy and intermittent fasting: the connection for cancer therapy?


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