What does intermittent fasting consist of?

Each season brings with it a new nutritional trend to lose weight. Now everyone talks about intermittent fasting. “It is important to note that fasting cannot be considered a diet, since this guideline implies restricting food for a certain time, while the concept of diet refers to the habitual intake of food and beverages”, distinguishes Ana Zugasti, from the Nutrition Area of the Spanish Society of Endocrinology (SEEN) .

“Intermittent fasting consists of establishing more specific time intervals for meals and between 12 and 16 hours of fasting per day,” says Gemma Tendero, member of the board of directors of the Official College of Dietitians and Nutritionists of the Valencian Community (Codinucova) .

Zugasti affirms that although the most common intermittent or sporadic fasting formulas are those of daily periodicity (at least 12 hours of fasting, the “16/8” pattern being the best known), there are others, such as weekly (generally one day or two a week fasting, followed or not). Within this second option, the most popular is the so-called “5: 2 diet”, which advocates normal eating five days a week and a severe reduction in intake (over 75%) the following two. Fasting on a monthly basis (fasting a couple of days in a row each month) is practiced to a lesser extent.

As for the schedule, how can intermittent fasting be arranged?

As described by the endocrinologist, one of the most common methods of intermittent fasting, known as 16/8, is a nutritional methodology based on intermittent fasting and consists of fasting for 16 hours (which usually includes 8 hours of sleep), allowing the intake during the following 8 hours . The most common feeding “window” is from 10 a.m. to 6 p.m.

Shopkeeper gives another example of the 16/8 method: “If the last meal is at 9 pm, the next meal could be at 1 noon, where the normal meal of this time of day could be made.”

What foods are recommended for meal hours?

“Usually there are no strict rules of what can be eaten in the allowed hours. It is assumed that with the fasting period the usual intake is reduced by 300 or 500 kilocalories a day, “says the SEEN expert.

For his part, Tendero highlights that “we must always start from a healthy diet. It is useless to do any type of dietary strategy if you do not start with a diet based on fresh food, especially vegetables and fruits. The amount should be that stipulated with the dietitian-nutritionist with whom they work, since it depends on the patient’s goals, needs and preferences. ”

As for the foods that are recommended, continues the expert from Codinucova, they are those that are part of a healthy diet: fresh, seasonal and preferably cooked at home. The base is vegetables and fruits, adding the rest of plant foods, legumes, seeds, natural dried fruits, whole foods (where the composition and the labeling indicate that they come from whole grains) and foods of animal origin (for those who do not are vegan) such as eggs, dairy, fish, shellfish, and meat.

Does it have health benefits?

Taking into account the results of scientific studies published so far, it seems likely that intermittent fasting may be as effective and safe as an equivalent calorie restriction diet. In other words, it can be a useful option, but only for some people ”, explains the specialist in Endocrinology and Nutrition.

Now, Zugasti continues, how much fasting is beneficial, and what the balance between long-term benefit or harm from insufficient calorie intake is, remains to be resolved. Evidence and long-term results are lacking to propose this type of dietary plan extensively. It would also be interesting to consider the possible added value of a physical exercise plan associated with this type of guidelines.

Storekeeper points out that intermittent fasting could increase insulin sensitivity or be helpful in high blood pressure . “It also serves to control the sensation of appetite and some studies suggest that it could play an important role in delaying aging,” he adds.

Risks and contraindications of intermittent fasting

Among the side effects of fasting are “headaches, dizziness, difficulties in maintaining concentration, alteration of other illnesses, or absorption of medications. Likewise, there may be nutrient deficits depending on the fasting time and the composition of the diet that is consumed in the allowed hours ”, Zugasti warns. Storekeeper insists that if not done under supervision there may be nutritional deficiencies, especially vitamins and minerals.

The SEEN expert says that it should be borne in mind that “stopping eating does not educate to learn how to do it and maintain a healthy diet. Also, in some vulnerable people it could trigger an eating disorder . ”

Another risk is that “since it has not been eaten for a certain number of hours or if the fast has been carried out several days during the week, it can give the sensation that you can eat anything, thus ending up eating products with high density Caloric and low in essential nutrients, such as snacks , pastries and junk food . ” So suggests Storekeeper.

Can it cause a lack of energy at certain times of the day? If you take advantage of the hours of sleep to be part of the fast and do not practice an important physical activity, it does not have to happen.

People who have problems with cholesterol , blood pressure, diabetes or heart disease, or pregnant or lactating women, children and adolescents, the elderly and people with eating disorders should always consult a specialist before adopting an intermittent fasting diet.

Regarding the cases in which intermittent fasting is in principle contraindicated, the experts cite the following:

  • People who have or have had an eating disorder.
  • People with a tendency to stressand anxiety .
  • People with migraines.
  • People with low weight.
  • Women pregnantor full breastfeeding .
  • People with type 1 diabetesor liver or kidney failure .
  • People with cholesterol, blood pressure or heart problems.
  • The children, adolescents and elderly


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