Does the 5:2 diet actually work?

5-2-dietThe 5:2 Diet is a pattern of eating that utilizes regular fasting as a quick, safe way to drop extra weight.

Also known as the “Fast Diet,” the protocol is classified as intermittent fasting, and is the most popular variation of this approach today.

Developed by a British doctor, the program gained attention through coverage by journalist Michael Mosley, and has been found effective as well as providing a list of health benefits.

There are no food restrictions, and counting calories is only necessary on two days of the week; because it’s more of an eating pattern than a diet, it is easier for many people to stick with the plan. (1)

Here are the basics:

  • Eat normally for 5 days of the week
  • Choose 2 days when you will eat only 500 (women) or 600 (men) calories total
  • Include at least one normal day in between the low-calorie days

It’s that simple.

The 500/600 calorie days are based on an estimated quarter of what the body’s daily needs are.

The trick is to keep food intake at truly normal levels when you’re not cutting back. Obviously bingeing or overeating after a fasting day will defeat the purpose, which is to reduce the overall number of calories you consume over a week’s time.

How It Works

There are several different approaches people have used successfully, and the ability to customize the diet to work for you is one of the best features of this way of eating.

For example, Monday and Thursday are the most common days chosen for fasting; this leaves 2 or 3 days in between for normal eating, and no need to do things any differently on the weekend than usual.

Another option is picking Tuesday and Thursday for fast days, leaving four days in a row to eat normally.

Some people find it easier to wait as long as possible to eat on a fast day, skipping breakfast and splitting the minimal amount of calories between two meals.

Others prefer to eat three times daily, keeping meals (or snacks) small and spreading them out over the day to minimize feelings of hunger.

Again, the most important aspect of following this eating plan is making certain you don’t compensate for the low-calorie days when you’re eating normally.

Intermittent Fasting Yields Health Benefits Beyond Weight Loss

The 5:2 diet hasn’t been scrutinized as a specific approach, but studies show intermittent fasting can have a range of benefits for overall health. (2, 3)

First and most importantly, many people find it easier to stay with the diet than other plans that are more restrictive in nature. (4, 5)

Insulin resistance is a growing health issue that can lead to diabetes and other metabolic disorders; insulin levels can be positively impacted by intermittent fasting. (6, 7)

One study confirmed that weight loss on the 5:2 diet was comparable to restricted calorie diets, as well as verifying reduced insulin levels. (8)

Another intermittent fasting plan based on reducing calories on alternate days has been studied more extensively, and results have been excellent. (9)

This approach, which could be called the 4:3 diet, lowers insulin levels, and may also have beneficial effects on seasonal allergies, menopausal hot flashes, cardiac arrhythmia, and asthma. (10, 11)

Check out these results from a 3-month randomized, controlled trial comparing the outcomes of subjects following the 4:3 diet to those who ate normally: (12)

  • Weight loss of about 11 pounds
  • Fat mass reduction of nearly 8 pounds
  • Triglycerides dropped by 20%
  • LDL cholesterol particles increased in size (a positive change)
  • C-Reactive Protein (CRP) levels dropped (an inflammatory marker)
  • Leptin levels dropped by up to 40%

Intermittent fasting through using a plan like the 5:2 diet or the 4:3 diet is effective for weight loss only if the calories you save on fasting days aren’t replaced on normal eating days. (13, 14) Protocols similar to the 5:2 diet look promising. (15)

Some participants drop up to 8% of body weight over 24 weeks, and well as up to 7% of waist circumference. (16)

This translates to a respectable amount of potentially harmful belly fat lost.

Another benefit of intermittent fasting is that much less muscle mass is lost as compared to traditional diets restricting caloric intake day after day. (17, 18)

Similar to other diets, the 5:2 plan can yield even more dramatic results when combined with endurance or strength training, as well as other forms of exercise. (19)

Planning Meals on Fasting Days

Foods high in protein and fiber are the best options for fast days, because you’ll feel more satisfied for the amount of calories you consume.

Many people find soups fit the program well. Studies show eating soup results in a higher level of satiation than when the ingredients are eaten separately. (20, 21)

Try some of these ideas for fast days:

  • Lean meat or grilled fish
  • Eggs
  • Soups low in calories, like tomato, vegetable or miso
  • Yogurt with fruit, preferably berries
  • Double servings of vegetables
  • Cauliflower rice
  • Black coffee or tea
  • Sparkling or regular water

It’s common to feel ravenously hungry the first few times you do a fast day, but the consensus is that after an adjustment period, it becomes much more manageable for most people.

Keeping busy helps, and it may be wise to plan ahead with low-calorie snacks available in case you feel weak, slow or faint.

Some people don’t adjust, and if you’re having trouble, you may want to talk with your doctor about the advisability of following the plan.

The 5:2 Diet Is Not For Everyone

If you have a history of frequent overeating, bingeing, or other eating disorders, this isn’t the diet for you.

Here are some other circumstances that would make intermittent fasting inadvisable:

  • Anyone who is sensitive to drops in blood sugar levels
  • Pregnant or nursing mothers
  • Women trying to conceive, especially those with fertility problems
  • Those who are underweight, malnourished, or have nutrient deficiencies
  • Patients diagnosed with type 1 diabetes
  • Children and teenagers

Some women report their menstrual periods stop during intermittent fasting, so caution should be exercised, and it’s best to stop the diet if any adverse effects are experienced. (22, 23)

Summary: The 5:2 Diet can be a fast and effective plan to initiate metabolic improvements and drop excess weight for people who are in good general health and don’t have counter-indications such as those listed above.


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