Fasting & meal-timing approaches
Intermittent fasting
An umbrella term for alternating periods of eating with periods of fasting or marked energy restriction, including 5:2, alternate-day fasting and time-restricted eating.
What people typically eat
Normal, ideally balanced meals during eating periods; water, black coffee and plain tea during fasts.
What is restricted
When you eat rather than what, though what you eat still determines overall diet quality.
Why people try it
Weight loss without daily calorie counting, plus interest in metabolic and insulin-sensitivity benefits.
Realistic advantages
- Simple rules, many people find "when" easier than "what"
- Trials show weight loss comparable to daily calorie restriction
- The 5:2 pattern has been shown to improve insulin resistance
Realistic disadvantages
- Hunger, headaches and poor concentration during adaptation
- No demonstrated long-term superiority over ordinary calorie control
- Easy to overeat in the eating window and cancel the deficit
Strength of evidence
Moderate evidence
Growing trial base showing equivalence with standard calorie restriction; unique long-term benefits are unproven.
Key studies
- Trepanowski et al., JAMA Internal Medicine, 2017. Alternate-day fasting produced similar weight loss to daily calorie restriction, with higher dropout rates.
- TREAT trial: Lowe et al., JAMA Internal Medicine, 2020. A 16:8 eating window on its own produced no significant extra weight loss against three structured meals a day.
Likely cost and difficulty
Low cost; moderate-to-high difficulty during fasting periods.
Nutritional risks
Low for healthy adults; risk of undernutrition if eating windows are used badly.
Who should avoid it
Pregnancy, under-18s, eating-disorder history, and people on glucose-lowering medication without medical advice.
Is professional supervision advisable?
Advisable if you have diabetes or take medication that requires food.
References
Written by the Slimr editorial team. How we review diets.
