Intermittent Fasting
Changes when you eat, not what — from daily time-restriction to alternate-day fasting.
How It Works
Intermittent fasting (IF) restricts when you eat rather than what you eat. There are
several distinct protocols, and they aren't interchangeable:
16:8 time-restricted eating (TRE) — eat within a fixed daily window (e.g. noon–8pm),
fast the remaining 16 hours, every day.
5:2 — eat normally 5 days a week; on 2 non-consecutive days, restrict to roughly
500–600 calories.
Alternate-day fasting (ADF) — alternate between normal-eating days and
very-low-calorie (~500 kcal) fasting days.
Eat-Stop-Eat — one or two full 24-hour fasts per week, normal eating otherwise.
TRE restricts by clock time every day; 5:2, ADF, and Eat-Stop-Eat restrict by calendar day, with longer
full fasts on the restricted days.
The Research
IF is associated with weight loss broadly comparable to standard calorie restriction, plus some improvements in insulin sensitivity, blood pressure, and cholesterol in certain trials — but the long-term evidence is thinner than for Mediterranean or DASH, and several well-designed recent trials found no added benefit over calorie restriction alone. Both sides are worth knowing before you pick this over just tracking calories.
Overview: de Cabo R, Mattson MP. "Effects of Intermittent Fasting on Health, Aging, and Disease," New England Journal of Medicine, 2019. A narrative review of the metabolic mechanisms behind fasting and the human trial evidence available at the time.Read the review →
Null result: Lowe DA, Wu N, Rohdin-Bibby L, et al. "Effects of Time-Restricted Eating on Weight Loss and Other Metabolic Parameters in Women and Men With Overweight and Obesity: The TREAT Randomized Clinical Trial," JAMA Internal Medicine, 2020. In a 12-week RCT of 116 adults, 16:8 time-restricted eating produced no significant weight-loss advantage over eating three structured meals a day, and modestly reduced lean mass in the TRE group.
Read the TREAT trial →
Null result: Liu D, Huang Y, Huang C, et al. "Calorie Restriction with or without Time-Restricted Eating in Weight Loss," New England Journal of Medicine, 2022. In a 12-month RCT of 139 adults with obesity, adding an 8-hour eating window on top of calorie restriction gave no significant extra benefit for weight, body fat, or cardiometabolic markers versus calorie restriction alone.
Read the trial →
Comparing protocols: Elortegui Pascual P, Rolands MR, Eldridge AL, et al. "A meta-analysis comparing the effectiveness of alternate-day fasting, the 5:2 diet, and time-restricted eating for weight loss," Obesity, 2023. A network meta-analysis of 24 RCTs (n=1,768) found all three IF patterns produce weight loss broadly comparable to continuous calorie restriction — alternate-day fasting ranked marginally best, time-restricted eating ranked weakest — while cautioning the underlying evidence is short-term and inconsistent in design.
Read the meta-analysis →
What You Eat
IF doesn't restrict food types — only timing — so there's no food list to speak of. What matters most inside the eating window: enough total calories and protein (fasting isn't license to undereat, and it isn't license to overcompensate with ultra-processed food either), fiber and produce for satiety, and staying hydrated during fasting hours with water, black coffee, or plain tea (no added calories).
A Sample Day (16:8, noon–8pm)
Noon: eggs, vegetables, whole-grain toast.
3–4pm: Greek yogurt, fruit, and nuts.
7–8pm: lean protein, vegetables, rice or potatoes.
Water, black coffee, or plain tea are fine before noon and after 8pm.
Who It Might Suit
May suit people who find a fixed eating window easier to stick to than counting every meal, or who naturally skip breakfast anyway. Given the null results above against plain calorie restriction, it's worth choosing based on which approach you'll actually sustain, not because IF has a proven metabolic edge. It's not recommended without medical supervision for anyone with a history of disordered eating, people who are pregnant or breastfeeding, type 1 diabetics or anyone on glucose-lowering medication, or children.