The 5:2 diet is a modified version of Intermittent Fasting, which focuses on having structured days of the week where the user dramatically reduces caloric intake. More specifically, the user will continue with normal eating habits for 5 days of the week, but will schedule 2 days where caloric intake is lowered to 500-600kcal (500kcal for women, 600kcal for men).
Much like Intermittent Fasting, it is more of an eating routine as opposed to a diet. However, unlike traditional Intermittent Fasting, the 5:2 diet does require calorie counting on 2 days of the week, and therefore it is not as flexible regarding what and how much you eat.
In comparison to conventional dieting, which requires a small daily energy deficit, the 5:2 diet focuses more on creating the same weekly energy deficit by compensating less deficit days with a much-reduced energy intake on these days.
May be easier to stick to than conventional diets
At least for many people, having fewer days to focus on restrictive eating may lead to greater long-term commitment and progress.
Although scientific data on the diet is rare, subjectively it appears people are more willing to stick to reduced frequency of dieting days, albeit these days having more restrictive and ‘extreme’ protocols, as opposed to conventional dieting methods. Despite limited data, scientific evidence does support this theory, with a meta-analysis confirming that studies on obese individuals have shown greater patient compliance with Intermittent Fasting compared to traditional nutritional approaches .
In addition, a study that used a similar approach to 5:2, put subjects on alternate-day fasting diet (consuming 25% of energy needs on the fast day and normal food intake the following day), and led to an average 5.6kg of weight loss after 8 weeks with a 3% body fat reduction . Furthermore, despite having a higher frequency of fasting days compared to the 5:2 diet, subjects still reported a daily adherence rate of 89%.
A variety of health improvements
The list of health benefits linked to Intermittent Fasting in the scientific literature is vast, although the evidence is still new and needs to be explored further for clarification.
The main reported benefits are increased insulin sensitivity, stress resistance (increased resistance of neurons in the brain to excitotoxic stress), reduced morbidity and increased life span . Other reported advantages include improved glucose regulation and lipid metabolism (reduced visceral fat tissue and increased plasma adiponectin level), as well as a reduction in oxidative stress, cell damage, and inflammation .
Recent evidence also shows Intermittent Fasting significantly reduces LDL cholesterol, increases HDL cholesterol, and positively influences gut health and microbiota by increasing good bacteria such as YS2 and RF32, whilst reducing bad bacteria .
It is worth noting that studies on intermittent fasting are usually conducted on animal models and do not always account for the influential effects of weight loss on health improvements.
Does not limit food choice
Unlike most popular diets, the 5:2 diet does not give any unnecessary restrictions on what you must eat or avoid. This can have a positive impact on flexibility, convenience and adherence. However, with 2 days being limited to ~500 calories, users must be aware that although not limited by food choice, it is wise to choose extremely low calorie, high volume, high fiber, protein-rich foods in order to make the best of a bad scenario and limit hunger.
Overeating on ‘normal’ eating days
People may be over consuming on their regular eating days to compensate for the massive reductions in food intake on fasting days (this might be without realising!).
In a person who does not track caloric intake, energy intake is largely dictated by food choice, leptin levels, and hunger. Leptin, a hormone made by adipose cells that helps to regulate energy balance by inhibiting hunger, may be decreased after a day of fasting and therefore cause a noticeable increase in hunger the following day.
Therefore, users who typically eat until they feel satisfied and satiated may be overeating on normal days and subsequently consuming the same weekly energy intake compared to their normal eating routines. If weight reduction does not occur from this diet, it may be worth tracking caloric intake on normal days to ensure complete control of your diet. Be mindful that you will also make better progress if you do not treat non-fasting days as ‘off’ days, making an effort to stick to whole foods and not overindulging in treats or snacks.
Poor physical and mental performance on fasting days
The 5:2 diet is not built for athletes or exercise enthusiasts.
This is due to it not addressing performance maintenance which is an essential component to achieving sustainable fat loss whilst preserving muscle tissue and strength. Short and long-term energy intake and carbohydrate intakes are one of the main determinants of aerobic and anaerobic exercise performance, with low intakes significantly impacting strength and endurance in a negative way .
Low energy intakes, specifically carbohydrates, reduce the energy capacity of muscle tissue by causing low glycogen levels, decreasing the rate of glycolysis (conversion of glucose to pyruvate), and decreasing blood glucose levels.
Consuming only 500 calories on a single day will commonly affect performance the same day, as well as the following day, although this is largely dictated by individual variance. Studies are also available showing the negative impacts low carbohydrate intakes have upon focus, concentration and memory abilities . Reduction in mental performance not only further impacts physical performance, but it can lower overall well being and one’s content and satisfaction whilst dieting.
Who should run this diet?
The 5:2 diet is great for the average person looking to lose some weight whilst keeping flexibility in their life. For most individuals, this diet will successfully shed the pounds as long as users are actively avoiding overcompensation on non-fasting days. The diet should not be considered extreme, despite incorporating extreme regimens on a minority of days, and does allow people the freedom to eat all the foods they enjoy in moderate quantities.
The diet is not ideal for people who have a lifestyle that relies heavily on physical and/or mental performance (fitness, work etc) as some individuals may be significantly affected by the large energy deficits on fasting days. It is wise to see for yourself the extent to which fasting days affect your body and whether you consider the positives to outweigh the negatives.
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