Intermittent Fasting Not Losing Weight? What to Check First

Intermittent fasting and not losing weight usually means the fast has stopped creating a calorie gap. The fasting window helps some people eat less, but the timing on its own does not burn extra fat. So when the scale is stuck, the useful question is where the extra calories are coming from. The checks below go from the quickest to the slowest, and the first one is whether you have a problem at all.

Why you’re not losing weight on intermittent fasting

Weight loss on intermittent fasting comes from eating less than you burn. The timing alone adds little. In a 12-month trial of 139 adults with obesity, an 8-hour eating window plus calorie cutting lost 8.0 kg. Calorie cutting alone lost 6.3 kg, and the gap was not statistically significant. A 2025 BMJ review pooling 99 trials put intermittent fasting level with ordinary calorie cutting for weight. The evidence for this is moderate, as the review found only “some indication” across those trials.

That explains why intermittent fasting doesn’t work for everyone. Some people eat less inside a window without trying. Others eat the same amount in fewer, larger meals, and their weight stays put. The trials are covered in more detail in the weight-loss evidence guide.

Is the scale showing fat or water?

Weight can swing from day to day with water, so check the trend before you change anything. Your body stores carbohydrate as glycogen, and each gram binds about 3 to 4 grams of water. A carbohydrate-heavy meal after a few lower-carbohydrate days refills those stores, so the scale can jump overnight without any fat gain.

To see past the noise:

• weigh yourself at the same time each day, after the toilet and before eating;
• compare weekly averages, not single days;
• measure your waist at the same spot once a week, because waist size can change when weight doesn’t.

The signs that intermittent fasting is not working are a flat weekly average and an unchanged waist over several weeks. If you see both, the next checks apply.

Check your real fasting window

A 16:8 plan can shrink to 14:10 without you noticing. Dinner slips from 7 pm to 8:30 pm, and breakfast moves from 11 am to 10:30 am. Tastes while cooking, a child’s leftovers and a milky coffee at 9 am all open the window early.

For one week, write down the time of your last bite each night and your first bite or caloric drink each morning. If the real fast is two hours shorter than the plan, set a fixed time for your last meal. Each schedule’s eating hours are set out side by side in the schedule comparison.

Drinks and snacks that add up

Calories you drink are easy to miss. Two or three milky coffees, or a glass of wine each evening, can use up the whole calorie gap from a 16:8 schedule. The table gives typical figures for common add-ons.

Item	Typical calories
Milk in coffee, 1 tablespoon (15 ml)	about 6 to 9
Double (heavy) cream, 1 tablespoon	about 50
Butter and MCT oil coffee (1 tbsp of each)	about 200 to 230
Red wine, 150 ml (5 fl oz) glass	about 125
Wine at 12%, 175 ml glass	up to about 160
Regular beer, 355 ml (12 fl oz) can	about 150
Almonds, 30 g handful	about 170 to 180
Honey, 1 tablespoon	about 64
Sugar, 1 teaspoon	about 16

Alcohol also slows fat burning while your body clears it. In a study of 8 men given 24 g of alcohol, whole-body fat burning fell by 73% for several hours. That evidence is early (a small human study). Drinks with close to zero calories are in the fasting drinks list.

Compare what you eat with your maintenance calories

Your maintenance calories are what you burn in a day. The TDEE calculator estimates them from your age, height, weight and activity. Its fat-loss figure is maintenance minus 20%, which is this site’s own rule. Obesity guidelines usually prescribe a daily deficit of 500 to 750 calories instead.

Worked example, from the TDEE calculator. Enter a woman aged 40, 168 cm tall, 80 kg (176 lb) and sedentary. Her maintenance comes out at about 1,787 calories a day. The calculator’s fat-loss figure for her is about 1,429 calories. If a week of notes shows she averages 1,800 calories, she is eating at maintenance, and her weight will hold.

The calculator never shows a target below 1,200 calories for women or 1,500 for men. Those are the lowest usual targets in the 2013 American obesity guideline. Every estimate can be off for one person, so treat it as a starting point and adjust from your weekly averages.

Will you keep losing weight with intermittent fasting?

Weight loss slows as you go, because a lighter body burns less. In the same example, at 72 kg instead of 80 kg her maintenance falls to about 1,691 calories a day. Meals that left a gap of about 360 calories at the start now leave a gap of about 260. That shrinking gap is one cause of a weight loss plateau while intermittent fasting.

The body’s response to eating less is also slow to settle. In modelling work, weight took about a year to reach half of its eventual change. So a straight-line forecast overstates later losses. Work out your maintenance again after every few kilograms lost, and expect the weekly drop to shrink.

Sleep, medicines and health conditions

Short sleep makes hunger harder to manage. In a small trial of young men, cutting sleep lowered leptin (a fullness hormone) by 18% and raised ghrelin (a hunger hormone) by 28%. That evidence is early (a small human study).

Some conditions and medicines can cause weight gain. The conditions include polycystic ovary syndrome (PCOS), Cushing’s syndrome and an underactive thyroid. The medicines include some for epilepsy, depression or psychosis, steroids, insulin and sulfonylureas. Keep taking prescribed medicines as directed, whatever your fasting plan. If your weekly averages stay flat for about eight weeks while your notes show a real deficit, see a doctor. That eight-week point is this site’s suggestion, not an official limit.

Should you fast longer or exercise fasted?

You may be tempted to stretch 16:8 to 20:4, but a longer fast adds little on its own. In a 2025 review of 99 trials, alternate-day fasting lost slightly more than continuous calorie cutting (about 1.3 kg), mainly in trials under 24 weeks. The other fasting patterns gave similar results. Training before your first meal does not seem to add fat loss either. In one 4-week trial of 20 young women on the same diet, fasted and fed cardio gave similar changes in body composition. That is early evidence.

If you do lengthen your fasts past 24 hours, ask a doctor first. Step back from fasting altogether if it fills your thoughts or the scale is driving your mood. The same applies if a fast often ends in a binge. Talk to a doctor about it. In an emergency, dial your local emergency number: 999 in the UK, 112 in the EU, or 911 for the US and Canada. The website findahelpline.com lists free helplines for most countries.

For each likely cause, its fix and the point to involve a doctor, open the “Not losing weight” section of the fasting troubleshooter.