Is fasting an easier way to lose weight?
Not in the way the popular version of the claim suggests. In this exploratory analysis of a randomized trial in 209 adults with obesity, intermittent fasting and daily calorie restriction both produced more weight loss than standard care, but the group that counted calories every day showed the larger improvements in eating behaviour. Fasting worked. It just did not work by making eating feel less demanding.
That distinction matters more than it sounds. Losing weight is hard, but sticking with a diet is often harder, and the psychological side of dieting is rarely measured. This analysis set out to see whether a fasting pattern and daily calorie cutting change eating behaviour, mood, sleep, and quality of life in the same way, or through different routes.
What the researchers tested
The trial randomized 209 adults with obesity in a 2:2:1 ratio to three groups. The average age was 58 with a standard deviation of 10 years, average body mass index was 34.8 with a standard deviation of 4.7, and 57 percent were female.
One group followed intermittent fasting plus early time-restricted eating. On three non-consecutive days each week they ate 30 percent of their energy requirements between 8 a.m. and noon, then fasted for 20 hours. On the remaining days of the week their intake was not restricted at all. A second group did continuous calorie restriction at 70 percent of energy requirements, the familiar approach of cutting calories every single day. The third group received standard care, meaning healthy eating guidelines at baseline and nothing further.
Both diet groups received nutritional support every two weeks. The intervention ran for six months, followed by 12 months of follow-up. Eating behaviour, mood, sleep, and quality of life were assessed with validated questionnaires at months 0, 2, 6, and 18, and the researchers ran a mediation analysis to test whether changes in eating behaviour explained the weight loss.
What the data show
Both diet groups lost more weight than standard care at month 2 and at month 6. On that measure, fasting and daily calorie restriction both did their job.
The eating behaviour results went the other way. Dietary restraint, meaning deliberate control over what you eat, rose more in the calorie restriction group than in either the fasting group or standard care at months 2, 6, and 18. Calorie restriction also produced larger reductions in disinhibition, the tendency to lose control of eating in response to food or emotion, and in feelings of hunger at month 6.
The mediation analysis found no detectable effect of change in dietary restraint on weight loss. Disinhibition did appear to mediate the effect in the calorie restriction group, accounting for 15 percent of the total treatment effect. The authors concluded that both approaches induce weight loss but potentially act through distinct behavioural pathways, with disinhibition playing a more prominent role in calorie restriction.
Dr. Kumar’s Take
The interesting result here is not that fasting worked. It is that the two diets appear to reach the same place by different roads. Calorie restriction shifted how people related to food more than fasting did: more restraint, less disinhibited eating, less hunger. If your eating problem is loss of control around food, that difference may be the one that decides which plan holds up for you.
I would not read this as fasting being the lower-effort option. That is the marketing claim, and this analysis does not support it. What it does support is that a schedule with three restricted days a week and unrestricted eating in between can take weight off in adults with obesity, which is a reasonable thing to offer someone who has failed at daily counting.
I also note that both diet groups received nutritional support every two weeks. Standard care got a handout at the start. Some of the gap between them belongs to that support, not to the eating pattern.
Who might benefit most
This approach may suit people who have repeatedly abandoned daily calorie counting. A plan built around three restricted days a week, with normal eating in between, is a different structure, and structure is personal. But if disinhibited eating is your main problem, the behavioural findings favour the daily calorie approach.
The fasting schedule tested here was demanding: 30 percent of energy requirements in a morning window, then 20 hours without food, three days a week. People with diabetes, those on blood sugar or blood pressure medication, pregnant women, and anyone with a history of disordered eating should talk to a doctor before attempting fasts of that length. What worked under biweekly supervision needs care when copied at home.
Practical Takeaways
- Both intermittent fasting and daily calorie restriction produced more weight loss than standard care at two and six months, so the choice between them is about fit, not about which one works.
- The fasting pattern tested was not a daily eating window. It restricted intake on three non-consecutive days a week and left the other days unrestricted.
- If losing control around food is your main difficulty, note that daily calorie restriction produced the larger reductions in disinhibition and hunger, and that disinhibition accounted for 15 percent of its treatment effect on weight.
- Both diet groups received nutritional support every two weeks. Build some form of regular accountability into whichever plan you pick.
- Talk to your doctor before starting 20-hour fasts if you take medication for blood sugar or blood pressure, since fasting can affect both.
Related Studies and Research
- 4-hour vs 6-hour time-restricted feeding: effects on sleep and weight loss
- Time-restricted eating improves sleep, mood, and quality of life in overweight adults
- Mindfulness meditation for chronic insomnia: randomized controlled trial results
- Can a daily probiotic ease depression in older adults?
FAQs
Is intermittent fasting better than counting calories for weight loss?
In this trial, both approaches produced greater weight loss than standard care at months 2 and 6. Where they differed was in eating behaviour: calorie restriction increased dietary restraint more at months 2, 6, and 18, and reduced disinhibition and hunger more at month 6. The authors’ reading is that the two diets work through distinct behavioural pathways rather than one being superior.
What does the 8 a.m. to noon eating window actually mean?
It applied on three non-consecutive days each week, not every day. On those days participants ate 30 percent of their energy requirements between 8 a.m. and noon, then fasted for 20 hours. On the rest of the week their eating was not restricted. So this was intermittent fasting combined with early time-restricted eating, not a daily short eating window.
Does the way a diet changes your eating behaviour matter for results?
In this trial it did, at least for one behaviour. Change in dietary restraint showed no detectable mediation of weight loss, so simply reporting more deliberate control over food did not explain the results. Disinhibition was different: it appeared to mediate the effect of calorie restriction on weight loss, accounting for 15 percent of the total treatment effect. That suggests reducing loss of control around food is doing part of the work in a daily calorie plan.
Bottom Line
In 209 adults with obesity, both intermittent fasting with early time-restricted eating and daily calorie restriction produced more weight loss than standard care over six months. The fasting arm restricted intake on three non-consecutive days a week and left the other days free. Calorie restriction produced the larger changes in restraint, disinhibition, and hunger, and disinhibition accounted for 15 percent of its effect on weight. Two workable routes, reached differently, and worth discussing with your doctor before you commit to long fasts.
