Intermittent fasting is currently one of the world’s most popular diet trends promoting quick weight loss. This pattern involves a cycle of eating followed by a cycle of fasting. The popularity of intermittent fasting might be because of the fact that your diet doesn’t fundamentally change ‘what’ you eat but ‘when’ you eat. In addition, there are six types of fasting one can pick from.
16/8 is the most practiced intermittent fasting, which promotes 16 hours of fasting followed by 8 hours of eating window. During the eating window, one can take two to three equally proportionate meals or two heavy meals and three small snacks. The other more popular method is the 5:2 intermittent fasting diet that involves regular eating for five days a week and restricting calorie intake to 500–600 calories for two days. Eat-stop-eat method of intermittent fasting involves a complete 24 hours of fasting once a week. Water, black coffee, zero-calorie drinks are allowed during fasting. In this method, it’s important to fuel up with nutritious meals before starting the fast to prevent hypoglycemia. Alternate Day Fasting (ADF) is another popular form of intermittent fasting that promotes one day fasting followed by one day of eating. A modified version of ADF allows you to eat about 500 calories on the days of fasting.
According to many nutrition researchers, the safety and efficacy of these methods are yet to be established and accepted universally as a sustainable solution for weight loss or preventing diabetes. However, several studies have reported beneficial outcomes of intermittent fasting in weight loss and insulin resistance.
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Weight loss and fat loss
Fasting decreases insulin level, increases human growth hormone and the level of norepinephrine. All these combined facilitates fat and weight loss. A study involving 59 obese patients who followed eight-week alternate day fasting protocol reported 3.9 kg weight loss. Loss of fat mass and visceral fat mass was also documented.
Another study by Takayuki Teruya and colleagues have reported significant improvement in metabolic markers in volunteers who fasted for 34 to 58 hours. Higher metabolic rate is associated with expedited weight loss.
A review found three to eight per cent of weight loss in participants who followed alternate day fasting for three to 24 weeks. This study also reported four to seven per cent of visceral fat loss within six to 24 weeks.
Intermittent fasting in combination with calorie restriction is found to be effective for weight loss and improved heart health as reported by Klempel and colleagues. The authors conducted an eight-week-long Randomized Controlled Trial, involving 54 obese women and observed a significant body weight reduction ranging between 2.5 to 3.9 kg. This study also reported 1.9 to 2.8 kg fat mass loss among the participants under investigation.
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Lowers the risk of Type 2 diabetes
Type 2 diabetes is a metabolic disorder which is an outcome of prolonged insulin resistance. Intermittent fasting and Alternate Day Fasting found to reduce insulin resistance and demonstrated a remarkable reduction in blood sugar level as well.
A study reported three to six per cent reduction in fasting blood sugar within 8 to 12 weeks in people living with prediabetes. In the same cohort, fasting insulin was decreased by 20 to 31 per cent.
The primary marker of measuring insulin sensitivity is known as homeostatic model assessment (HOMA-IR). In an ADF trial by Surabhi Bhutani and others, involving 64 obese patients, body weight was found to have be decreased by 4 per cent from baseline, which produced moderate reductions in HOMA-IR (9 per cent).
A randomised trial in 107 overweight patients assessing the effects of intermittent or continuous energy restriction on weight loss and metabolic disease risk markers found 27 per cent decline in HOMA-IR after 24 weeks of fasting two days per week. The study also reported a weight loss by seven per cent.
All these studies offer a promising scientific explanation that practicing intermittent fasting and ADF can be effective for the people with the initial stage of glucose intolerance and can prevent diabetes. These evidence also show that the best result in improving insulin sensitivity is found in people with highest weight loss. However, the number of these studies are limited and thus no conclusion can be drawn if regular calorie restrictive diet can be replaced with intermittent fasting or ADF as regimes to produce sustainable weight loss and/or type 2 diabetes risk reduction.
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The loopholes
Nutritionists think a long fasting period of 16 hours leads to binge eating during the eating hours in some people. This might lead to weight gain instead of weight loss. intermittent fasting doesn’t provide guidelines on what to eat. Often people tend to consume high calorific meals assuming that anything can be eaten during the eating cycle. Some people also experience mood swings, decreased cognitive functions that affect their work ability or overall performance. intermittent fasting might not be sustainable due to non-flexibility and reports a larger percentage of drop out at an early stage in comparison to regular calorie restrictive diets.
A 2019 study discusses unsupervised intermittent fasting can be very dangerous for people living with type 1 diabetes and in people who are on some diabetic medications.
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The bottomline
intermittent fasting and ADF have many health benefits proven in structured scientific studies. However, the evidence is limited and lacks a bigger sample size to prove the hypotheses for universal acceptance.
intermittent fasting diets often lack essential micronutrients due to restrictive eating windows.
Unsupervised practice of intermittent fasting may lead to more harm than help. If you want to try intermittent fasting consult a nutrition expert for the schedule and meal composition according to your nutritional needs because one size doesn’t fit all.
Subhasree Ray @DrSubhasree is Doctoral Scholar (Ketogenic Diet), Certified Diabetes Educator, Clinical and Public Health Nutritionist. Views are personal.
(Edited by Anurag Chaubey)