Counting calories can work for weight loss, but it can also feel like a constant negotiation with every meal, snack and serving size. For some people, that mental load may be one reason diets are hard to maintain.
A new randomized clinical trial from Adelaide University suggests intermittent fasting may offer a different path for some adults with obesity. In the study, intermittent fasting and continuous calorie restriction led to similar weight loss after six months, but participants appeared to get there through different psychological and behavioral routes.
The study, published in Clinical Nutrition, followed more than 200 adults with obesity for 18 months. It did not show that intermittent fasting was better than calorie restriction for weight loss. Instead, it suggests fasting may help some people lose weight in a way that feels less dependent on constantly monitoring food intake.
“While many diets can result in weight loss, they may be difficult to stick to and this makes keeping that weight off long-term more challenging,” said Professor Leonie Heilbronn from Adelaide University’s School of Medicine and the South Australian Health and Medical Research Institute. “The results of our study indicate intermittent fasting could offer an alternative pathway for people who find conventional dieting challenging.”
Participants were assigned to one of three groups: intermittent fasting, continuous calorie restriction or standard care with healthy eating guidelines. The intermittent fasting group consumed 30% of their energy needs between 8 a.m. and noon on three nonconsecutive days each week, followed by a 20-hour fast. On nonfasting days, they ate their regular diet.
The calorie restriction group was asked to eat 70% of their usual intake each day. The standard care group received healthy eating guidance but did not follow either of the more structured diet plans.
After six months, participants in both the intermittent fasting and calorie restriction groups lost about seven kilograms, or roughly 15 pounds. Participants in the standard care group lost about two kilograms, or about four pounds.
That finding is important because it means the fasting plan did not outperform calorie restriction in the amount of weight lost. The more interesting difference was how the approaches seemed to work.
People in the calorie restriction group reported that they had to consciously focus on restricting food intake and avoiding overeating. That improved sense of eating control accounted for 15% of their weight loss, according to the researchers.
People in the intermittent fasting group, however, did not report the same need to make major changes to their eating behaviors, such as calorie counting or constant monitoring of overeating. That suggests fasting may reduce the number of decisions some people have to make around food, at least within the structure used in this trial.
“Psychological and behavioural effects have a major influence on people’s abilities to adhere to diets. Intermittent fasting may help people achieve weight loss through ways that are less dependent on consciously restricting intake,” Heilbronn said.
The study also looked at mood, sleep and quality of life. Participants in both structured diet groups reported improvements in depression and well-being, even on fasting days.
That does not mean intermittent fasting is the right choice for everyone. The plan used in this study was specific: three low-energy mornings per week followed by long fasting periods. It is not the same as every popular fasting approach, such as skipping breakfast, eating only during an eight-hour window or fasting on alternate days.
Fasting may also be inappropriate for some people, including those with a history of eating disorders, pregnant or breastfeeding people, some people with diabetes, people taking medications that must be timed with food and anyone who has been advised by a clinician not to fast.
The study also focused on adults with obesity, so the findings should not be stretched to everyone trying to make small changes to their eating habits. And while the trial lasted 18 months, the main weight loss comparison highlighted in the release was at six months. Long-term maintenance remains one of the hardest parts of weight management.
Still, the findings point to a useful idea: the best eating plan may not be the one that looks most effective on paper. It may be the one a person can realistically follow.
For some, daily calorie tracking may provide helpful structure. For others, it may feel exhausting or unsustainable. Intermittent fasting may work for some people not because it is magic, but because it changes the framework. Instead of deciding how much to restrict at every eating occasion, some people may find it easier to follow clearer boundaries around when and how much they eat on specific days.
“Future trials should be designed to identify individuals who struggle to improve eating behaviours, as they may do better with intermittent fasting diets, enabling more personalised weight management,” Heilbronn said.
This work was supported by a National Health and Medical Research Council Project Grant. XTT was supported by an Australian Government Research Training Program Scholarship from The University of Adelaide.