What is The 5:2 Diet and How Does it Work?

Have you heard of the 5:2 diet? It's a form of the well-known intermittent fasting. Check out the advantages and disadvantages of applying it to your diet.
What is The 5:2 Diet and How Does it Work?
Maria Patricia Pinero Corredor

Written and verified by the nutritionist Maria Patricia Pinero Corredor.

Last update: 05 January, 2024

Intermittent fasting has become one of the most popular weight loss strategies. There are several ways to implement it, but one of the most recognized for its effectiveness is the “5:2 diet”. What is it all about?

In this type of fasting, it’s proposed to eat five days per week in a normal way and reduce total calories the other two days. In fact, this is also known as the “fasting diet” and became popular in 2012 as an adjuvant to control insulin resistance, blood pressure, and cholesterol levels.

Currently, there’s evidence that recognizes its positive effects on health. However, there are also studies that cast some doubt on it. So, what are its advantages and disadvantages? Let’s take a closer look.

How does intermittent fasting work?

During intermittent fasting, the body uses fat reserves instead of glucose for energy. This results in weight loss. Through its implementation, it’s possible to reduce caloric intake per week.

Trepanowki and other researchers suggest that the longer the fasting period, the more likely it is to decrease inflammation, obesity, and insulin resistance.

To be more precise, this strategy incorporates elements of the ketogenic diet and the concept of glycemic index. On normal days, it’s suggested to follow a low-carbohydrate diet. And while the schedules are varied, the 5:2 is one of the most widely used diets because of its advantages.

¿Cómo funciona el ayuno intermitente?
Intermittent fasting has become one of the most widely used strategies to combat the effects of metabolic syndrome.

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What is the 5:2 diet all about?

The 5:2 diet allows for normal eating or caloric intake commensurate with daily functions, for five days of the week. Reasonable portions of a wide variety of foods should be eaten. However, calories don’t have to be measured or counted.

No matter how many carbohydrates and how much protein some foods contain, the main rule is to respect the meal schedule. Now, the other two days of the week you have to make a restriction to 600 calories a day for men and 500 calories a day for women.

Of course, you have to be careful when activating this dietary model. For example, if during the five days off you eat foods loaded with calories, sugars, or processed foods, you may not lose weight, but quite the opposite.

During the two days of fasting, you have to decide if a small breakfast works better, or if you wait as long as possible to eat the first meal. Fasting represents a 25% reduction in total calorie intake.

The general recommendation is to spread calories over 3 meals. That is, eat 200 calories at breakfast, 200 at lunch, and 100 at dinner. It’s also valid to reduce them to 2 meals of 250 calories each.

On the other hand, it’s a good idea to reduce calories slowly during fasting. Thus, if your usual consumption is 1,800 calories, it can be reduced to 1,300 calories in the 2 days of fasting during the first week. After that, calories can be reduced to 500 or 600 calories.

What are the advantages of the 5:2 diet?

Like other forms of fasting, the 5:2 diet is associated with certain advantages. These are listed below.

It’s flexible

With the 5:2 diet, it’s possible to freely choose the days and times of fasting. In addition, there’s the freedom to distribute calories over breakfast, lunch, or dinner, or leave them for a main meal.

On the other hand, depending on commitments and obligations, fasting can be varied from one week to another, especially on weekends, days when family and social gatherings are more frequent.

It’s not an extreme diet

Unlike other more restrictive diets, it isn’t necessary to do complete 24-hour fasts or drink only tea, coffee, or water. The 5:2 fasting isn’t such a long process and decreases the feeling of anguish or anxiety that usually derive from stricter regimes.

All foods are allowed

It offers the possibility of including all types of food. Even so, the key is to avoid those foods with “empty calories and to prioritize those that are abundant in vitamins, minerals, proteins, and healthy grains.

It helps to take care of your health

According to some studies, the 5:2 diet is a form of intermittent fasting, which has health benefits. The journal Behavioral Science highlights its positive medium-term effects on fat reserves and adipocyte size.

It also has a favorable influence on insulin resistance and metabolism in obese and overweight people. Moreover, a review published in 2020 concluded that intermittent fasting helps reduce the risk of cardiovascular disease.

Improved weight control, hypertension, diabetes, and blood lipid profile were found. These findings relate to reducing oxidative stress and optimizing the release of ketones instead of sugar as an energy source.

However, other researchers think otherwise. Because of this, further studies of the 5:2 diet in humans are recommended to confirm the results.

It can be a motivating diet

Some studies show that the weight loss achieved with the 5:2 diet ranges from rapid to moderate, which can be motivating for the participant. However, they also explain that it may work for some, but not for others.

Possible disadvantages of the 5:2 diet

Despite its interesting advantages, the 5:2 diet has some disadvantages worth considering. Of course, it’s best to evaluate them in the company of a nutrition professional.

Initial adverse effects

The journal Behavioral Science also explains that during the first few days of fasting, the following symptoms may occur :

  • Intense hunger
  • Irritability
  • Fatigue
  • Weakness
  • Headaches
  • Mood swings
  • Difficulty sleeping

However, once the body adapts, these reactions may disappear. In general, when faced with these side effects, it’s recommended to drink water, rest, meditate, or practice some relaxation techniques.

The risk of overeating

As with other diets, there’s always a risk of overeating, especially when fasting. It’s possible that this may hinder the goals for weight loss or to restore health.

Food groups may be eliminated

It’s likely that on fasting days some food groups that balance the diet will be eliminated. When the diet is long-term, it may cause vitamin and mineral deficiencies.

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Your exercise plan may be put at risk

The exercise plan may not work completely, as little energy is consumed on fasting days. In addition, the participant may feel tired, fatigued, and with less attention span.

Disordered eating may be encouraged

Disordered eating may be encouraged on the two fasting days, as caloric intake is very low and difficult to maintain over time.

It may not be sustainable in the long term

The 5:2 diet does not include exercise and mind control for conscious and sustained eating within its plan. Therefore, strategies should be sought to supplement it.

Restricción de alimentos
It’s difficult for some people to sustain this type of fasting over the long term.

It isn’t appropriate for everyone

5:2 fasting may not be appropriate for sportspeople, athletes, or people who are moderately physically active, as the body needs energy to fuel activity. Fasting days are not at all favorable for these activities and may promote fatigue and poor performance.

Some hormones that increase hunger may be altered

The New England Journal of Medicine highlights that after a diet-induced weight loss, the person begins to feel hungrier as a form of compensation. This is achieved by an increase in some hormones that stimulate hunger.

When to consult a professional?

As we have mentioned before, this diet isn’t valid for everyone. Therefore, it’s necessary to consult a doctor or nutritionist in the following cases:

  • Low blood sugar values or diabetics
  • Children and adolescents
  • People with treated or untreated eating disorders
  • People with low weight
  • Women with fertility problems or who wish to become pregnant
  • Pregnant and nursing mothers
  • People with nutritional deficits
  • Those who tend to suffer from dizziness or fainting

It must be remembered that if the objective is to lose weight in the long or short term, it’s essential to be well-advised to choose the best diet. The professional will be able to determine the best strategies according to individual characteristics such as age, sex, health condition, and preferences, among others.

All cited sources were thoroughly reviewed by our team to ensure their quality, reliability, currency, and validity. The bibliography of this article was considered reliable and of academic or scientific accuracy.

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  • Tiffany A. Dong, Pratik B. Sandesara, Devinder S. Dhindsa, Allen L. Dollar, Pam R. Taub, Laurence S. Sperling. Intermittent Fasting: A Heart Healthy Dietary Pattern?  VOLUME 133, ISSUE 8, P901-907, AUGUST 01, 2020. DOI:https://doi.org/10.1016/j.amjmed.2020.03.030
  • Stockman, MC., Thomas, D., Burke, J. et al. Intermittent Fasting: Is the Wait Worth the Weight?. Curr Obes Rep 7, 172–185 (2018). https://doi.org/10.1007/s13679-018-0308-9
  • Harvie M, Howell A. Potential Benefits and Harms of Intermittent Energy Restriction and Intermittent Fasting Amongst Obese, Overweight and Normal Weight Subjects—A Narrative Review of Human and Animal Evidence. Behavioral Sciences [Internet] 2017;7(4):4. Available from: http://dx.doi.org/10.3390/bs7010004
  • Purcell, K., Sumithran, P., Prendergast, L.A., Bouniu, C.J., Delbridge, E., & Proietto, J. (2014). The effect of rate of weight loss on long-term weight management: a randomised controlled trial. The lancet. Diabetes & endocrinology, 2 12, 954-62 .
  • Mayoclinic. Estilo de vida saludable y pérdida de peso: 6 estrategias para lograrlo.  Disponible en: https://www.mayoclinic.org/es-es/healthy-lifestyle/weight-loss/in-depth/weight-loss/art-20047752.
  • Sumithran, P., Prendergast, L.A., Delbridge, E., Purcell, K., Shulkes, A., Kriketos, A.D., & Proietto, J. (2011). Long-term persistence of hormonal adaptations to weight loss. The New England journal of medicine, 365 17, 1597-604 .
  • Trepanowski, J. F., Kroeger, C. M., Barnosky, A., Klempel, M., Bhutani, S., Hoddy, K. K., Rood, J., Ravussin, E., & Varady, K. A. (2018). Effects of alternate-day fasting or daily calorie restriction on body composition, fat distribution, and circulating adipokines: Secondary analysis of a randomized controlled trial. Clinical nutrition (Edinburgh, Scotland)37(6 Pt A), 1871–1878. https://doi.org/10.1016/j.clnu.2017.11.018
  • Arnason TG, Bowen MW, Mansell KD. Effects of intermittent fasting on health markers in those with type 2 diabetes: A pilot study. World J Diabetes 2017; 8(4): 154-164 [PMID: 28465792 DOI: 10.4239/wjd.v8.i4.154]

This text is provided for informational purposes only and does not replace consultation with a professional. If in doubt, consult your specialist.