Intermittent Fasting Is Beneficial Even without Calorie Restriction

Recent studies suggest that intermittent fasting may produce weight loss of 1 - 4% even without calorie restriction. However, more comprehensive studies are needed to support these promising findings, because most studies conducted so far have included few participants.

Before examining studies evaluating intermittent fasting’s effects on weight loss, let us briefly review this dietary pattern:

Intermittent fasting generally follows a 16/8 eating pattern. Food intake is restricted to an 8-hour window, with no food consumed for 16 hours apart from calorie-free liquids (water, herbal tea and similar drinks).

Because this dietary pattern involves prolonged fasting, the body uses fatty acids and ketone bodies rather than glucose as its energy source. This is thought to accelerate weight loss.

Some research argues that the most effective intermittent fasting pattern stops food intake early in the day. In this model, eating begins at 8 in the morning and continues until 16.00 or 18.00. After 8 or 10 hours of food intake, nothing containing calories is consumed.

Studies of Weight Loss with Intermittent Fasting

Intermittent fasting is also thought to have possible negative effects on weight loss, including the concern that prolonged fasting may cause muscle loss. Comprehensive studies are therefore needed to fully understand this dietary pattern’s advantages and disadvantages. Let us examine systematic analyses and meta-analyses compiling small studies of intermittent fasting and weight loss:

2020 was the year a systematic analysis published in “Nutrients” examined research conducted between 2014 and 2020 on “Intermittent Fasting and Weight Loss”, evaluating 23 studies. Of these, 80% applied calorie restriction, while 20% did not. The review found that intermittent fasting led to an average loss of 3% fat mass regardless of calorie restriction. This indicates that intermittent fasting affects weight loss even without calorie restriction (Source 1).

2020 also saw publication in “Nutrients” of a meta-analysis examining the relationship between intermittent fasting, weight loss and general health, which included 19 studies. It found an average weight loss of 0.38 kg, a reduction in body-fat percentage of 0.55% and a fat-mass loss of 1.27 as reported in the study (2).

However, neither of the above 2 studies used a control group. They therefore provide no data for comparing the rate of weight loss with intermittent fasting.

Unlike the above 2 studies, a study published in 2019 in “BMC Gastroenterology” compared the rate of weight loss with intermittent fasting and a control group. In this study of people with fatty liver disease, there were 271 participants, observed for 12 weeks, during which the study compared 2 intermittent fasting patterns with a control diet. Let us examine the content of the participants’ dietary patterns:

• Alternate-day fasting: 24 hours of fasting were followed by a 24-hour healthy-eating pattern. On feeding days, participants consumed 75% of their required energy. The diet was also designed to provide 30% of energy from fat, 15 from protein and 55% from carbohydrates. Calorie-free drinks such as coffee and tea were allowed on fasting days.
• Time-restricted fasting: 16 hours of fasting were followed by 8 hours of healthy eating. Participants were given no dietary advice for the 8-hour eating window. Calorie-free beverages were allowed during the 16-hour fasting period.
• Control group: Participants consumed 80% of their required daily energy.

Study results were obtained at week 4. They showed that participants following intermittent fasting had lost more weight than the control group.

“Alternate-Day Fasting” participants lost an average of 4.56 kg, “Time-Restricted Fasting” participants lost 3.62 kg, and “Control” participants lost 2.24 kg on average.

12 weeks later, measurements again showed the best weight and fat loss with the “Alternate-Day Fasting” diet, while “Time-Restricted Fasting” also produced satisfactory results.

In addition to weight loss, the “Alternate-Day Fasting” diet was the most effective at lowering total cholesterol. However, there were no differences between diets in muscle mass, HDL, LDL, fasting insulin, glucose, liver enzymes or systolic/diastolic blood pressure (3).

Another study was published in 2020 in “Jama International Medicine”. It compared “Time-Restricted Fasting” (the 16/8 model) with a diet involving 3 meals per day. In “Time-Restricted Fasting,” participants ate between noon 12.00 and 20.00 in the evening. The study involved 116 participants over 12 weeks. At the end of the study, participants following “Time-Restricted Fasting” lost an average of 0.97 kg, while those eating 3 meals lost 0.68 kg. There was no significant difference in weight loss between the diets. However, participants reported their food intake through answers to questions in a phone app, making it impossible to precisely calculate the daily energy consumed in the 2 dietary patterns (4).

Comment

Existing studies suggest that intermittent fasting may affect both weight loss and fat loss. It may also affect certain blood parameters that adversely influence general health, such as total cholesterol. However, participant numbers, durations and calorie controls in the studies were insufficient for a firm conclusion. More comprehensive studies examining intermittent fasting’s effects on both weight loss and general health may provide clearer answers.

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• Related topic: Intermittent fasting / fasting diet – EXCITING health effects (detailed)

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