Why am I gaining weight while fasting and working out? It’s one of the most frustrating things that can happen when you’re trying to get in shape. You’re skipping meals, you’re sweating through workouts, and the scale goes up instead of down. But here’s the thing. Weight gain during fasting and exercise is more common than you think, and it usually comes down to a few fixable reasons.
The good news is that this does not mean your effort is wasted. In many cases, your body is actually changing for the better even when the number on the scale says otherwise. Let’s break down exactly why this happens and what you can do about it.
Is the weight I’m gaining actually fat?
No. Most of the time, the weight you gain while fasting and working out is not fat. It’s water, muscle, or both.
When you start a new exercise routine, your muscles hold on to more water as part of the repair process. A study published in the European Journal of Applied Physiology found that resistance training causes temporary water retention in muscle tissue for up to 48 hours after a workout. This alone can add 1 to 2 kg on the scale.
Muscle is also denser than fat. So if you’re losing fat and gaining muscle at the same time, you might look leaner, feel stronger, and still weigh the same or even more. This is called body recomposition, and it’s a sign that things are working.
If your clothes fit better, your waist is getting smaller, or you can see more muscle definition, the scale is lying to you. Track your waist measurement and how your clothes fit instead of relying only on weight.
Can fasting actually cause weight gain?
Yes, if it leads to overeating during your eating window. This is one of the biggest mistakes people make with intermittent fasting.
Research from the American Journal of Clinical Nutrition shows that when calories are matched, there is no real difference in fat loss between time restricted eating and normal eating patterns. What matters is how much you eat in total, not when you eat.
The problem is that many people fast all day and then eat way too much in a short window. They feel starving after their fast, so they eat fast, eat big, and eat calorie dense foods. A 2020 study in the journal Obesity found that people who practiced intermittent fasting without tracking their food intake ate an average of 300 to 500 extra calories on fasting days compared to what they thought they were eating.
Fasting can work, but only if you still eat fewer calories than your body burns overall. If you’re gaining weight while fasting, you’re eating too much during your eating window. Full stop.
9 Steps To Shed 5–10kg in 6 Weeks
In only 90 minutes a week!
Includes an exercise plan, nutrition plan, and 20+ tips and tricks.
Without dead boring diets that are like watching paint dry
Without getting results at a snails pace
Does working out make you eat more?
It can, but the research is more interesting than you’d expect.
Studies show that exercise actually works as an appetite suppressant for many people. Research published in the journal Appetite found that people who exercise are more sensitive to satiety signals, which means they feel full faster and respond to those signals better than sedentary people.
There was a classic study from the 1950s that looked at Bengali workers across four activity levels. The sedentary workers actually ate more food than the lightly active and moderately active workers. From lightly active to heavily active, the workers almost perfectly matched their calorie intake to their energy output. The sedentary group couldn’t regulate their appetite at all.
But here’s where it gets tricky. While exercise can suppress appetite in the short term, some people do overcompensate. They finish a hard workout and think they “earned” a big meal or a treat. A 30 minute run might burn 300 calories, but a single muffin and a latte can replace all of that and then some.
The fix is simple. Track your food. Even just for a few weeks to understand how much you’re really eating. Research shows that people who log their food about three times per day are far more likely to lose weight than those who don’t track at all.
Is stress making me gain weight even though I’m dieting and exercising?
Yes. Stress causes your body to produce cortisol, and cortisol can lead to weight gain through several pathways.
A 2001 study found that women with high cortisol levels were more likely to eat high sugar foods and to overeat in general. Stress increases appetite, drives cravings for calorie dense foods, and can cause poor sleep, which makes everything worse.
When it comes to exercise, there’s a sweet spot. Training sessions that go past 60 minutes start increasing cortisol levels in a way that can actually slow down your recovery and results. This is why most exercise scientists recommend keeping resistance training sessions to about 50 to 60 minutes of real work after a 10 minute warmup.
If you’re training too hard, sleeping too little, and stressed out from work or life, your body is in a constant state of high cortisol. This can cause water retention, increased fat storage around the midsection, and a slower metabolism.
Reduce stress where you can. Meditation, therapy, and supplementation can all help. But the biggest lever most people can pull is getting more sleep, which brings us to the next point.
Can bad sleep cause weight gain even if I’m eating right and working out?
Yes. Sleep is one of the most underrated factors in body composition.
A 2010 study found that dieters who got a full night’s sleep lost more than twice as much fat as sleep deprived dieters, even when eating the exact same number of calories. That’s a massive difference from just sleeping more.
Bad sleep, which most researchers define as less than 7 hours per night, affects your body in three ways.
- It reduces leptin, the hormone that tells you you’re full after eating
- It increases ghrelin, the hormone that makes you feel hungry
- It activates the same brain receptors as marijuana, making your brain seek out high calorie foods
On top of that, a 2009 meta analysis found that poor sleep reduces non exercise activity thermogenesis (NEAT). NEAT is all the calories you burn through daily movement that isn’t formal exercise, things like fidgeting, walking around the house, and taking the stairs. When you’re tired, you subconsciously move less. You take the elevator instead of the stairs. You sit instead of stand. These small differences add up to hundreds of fewer calories burned per day.
Aim for 7 to 8 hours of quality sleep each night. It will lower cortisol, speed up recovery from workouts, and help your body burn fat more efficiently.
Am I eating too many calories without realizing it?
Almost certainly. This is the number one reason people gain weight while fasting and working out.
Your body doesn’t care about meal timing or workout schedules when it comes to fat storage. It only cares about energy balance. If you eat more calories than you burn, you gain weight. If you eat fewer calories than you burn, you lose weight. This is the law of thermodynamics, and no diet or exercise plan can override it.
The problem is that humans are terrible at estimating how many calories they eat. Research consistently shows that people underestimate their calorie intake by 30 to 50%. A meal you think is 500 calories might actually be 750 calories. Do that three times a day and you’re eating 750 extra calories without knowing it.
Here are 5 common calorie traps that catch people off guard.
- Cooking oils and butter. One tablespoon of oil has about 120 calories and 14 grams of fat. Most people use 2 to 3 tablespoons when cooking without measuring
- Sauces and condiments. Ketchup, mayo, salad dressing, and even “healthy” sauces can add 200 to 400 calories to a meal
- Drinks. A large latte with sugar has around 300 calories. Juice, smoothies, and soft drinks add up fast
- “Healthy” snacks. Nuts, dried fruit, granola, and protein bars are calorie dense. A small handful of almonds (about 30 grams) is 170 calories
- Post workout meals. Many people overestimate how many calories they burned during exercise and then eat back double that amount
Use a food tracking app for at least 2 to 4 weeks to get an accurate picture of what you’re actually eating. You will be surprised.
Does exercise burn fewer calories than I think?
Yes. Most people dramatically overestimate how many calories exercise burns.
A 30 minute jog burns about 250 to 350 calories for the average person. A 30 minute strength session might burn 150 to 250 calories. These are not huge numbers.
What makes it worse is something called energy compensation. Research shows that when you burn calories through formal exercise, your body subconsciously moves less throughout the rest of the day. Your NEAT drops. So if you normally burn 500 calories through daily movement like fidgeting and walking, and then you do a 500 calorie cardio session, your body might reduce your NEAT to 350 calories. You still get a net benefit, but it’s not as big as you thought.
This is why walking is actually more effective for fat loss than intense cardio for many people. Walking doesn’t trigger the same level of energy compensation, it doesn’t spike your appetite the way hard cardio does, and it’s much easier to do every day without needing recovery time.
Aim for 7,000 to 12,000 steps per day. A 30 minute walk adds about 3,000 steps and burns 100 to 200 calories. Over a month, that’s about an extra half a kilogram of fat loss with almost zero recovery cost.
Is my metabolism slowing down from fasting?
Probably not, at least not from short term fasting.
A 2012 study put subjects in an isolated respiration chamber for three days while eating either 3 meals per day or 14 meals per day with the same total calories. There was no difference in energy expenditure. Meal frequency does not speed up or slow down your metabolism in any meaningful way.
Where metabolism does slow down is when you’ve been in a large calorie deficit for a long time. If you’ve been eating very few calories for months, your body adapts by reducing energy expenditure. Your thyroid hormones drop, your NEAT drops, and your body becomes more efficient at using less energy.
This is called metabolic adaptation, and it’s a real thing. But it happens from prolonged severe calorie restriction, not from intermittent fasting done properly.
If you’ve been dieting hard for more than 3 to 4 months, consider taking a diet break. Eat at your estimated maintenance calories for 1 to 2 weeks, then resume your deficit. This can help reset some of those metabolic adaptations and make fat loss easier going forward.
Should I change my workout if I’m gaining weight?
The workout itself is probably fine. The issue is almost always nutrition.
That said, if you’re only doing cardio and no strength training, you’re missing out. Strength training builds muscle, and muscle burns more calories at rest than fat does. A study published in Medicine and Science in Sports and Exercise found that resistance training increases resting metabolic rate for up to 72 hours after the session.
Training your legs early in the week is smart because they are the largest muscle groups in the body. Training legs first sets off metabolic processes and hormonal events that carry you through the whole week in terms of elevated metabolism.
For fat loss, the best training approach combines.
- Resistance training 3 to 4 times per week, focusing on compound movements like squats, deadlifts, rows, and presses
- Walking 7,000 to 12,000 steps per day
- Optional interval cardio 1 to 2 times per week for 15 to 25 minutes
The one thing exercise does that nothing else can is improve your health markers independent of weight loss. Exercise improves insulin sensitivity, reduces inflammation, and lowers your risk of disease even if you don’t lose a single kilogram. Over 70% of people who lose weight and keep it off for years engage in regular exercise. Less than 30% of people who regain their weight exercise regularly.
How much protein should I eat to stop gaining fat?
More than you’re probably eating now.
Protein is special because about 20 to 30% of its calories get burned during digestion alone, which is more than double any other nutrient. Studies show that going from a low protein to a high protein diet raises your daily calorie burn by 4 to 5%. That’s the equivalent of a 10 minute jog every day without doing anything extra.
A 2005 study took a group of people and only asked them to double their protein intake. They didn’t tell them to eat less or change anything else. The participants naturally started eating fewer calories, and over 12 weeks they lost over 4.5 kg with almost all of it being pure fat. Protein is that filling.
To calculate your daily protein target, take your body weight in kilograms and multiply by 1.8. So if you weigh 80 kg, aim for about 144 grams of protein per day. Spread that across all your meals and snacks.
Good protein sources include chicken breast, fish, lean beef, eggs, Greek yogurt, cottage cheese, and protein powder. Include protein with every meal and every snack.
FAQ
How long does it take to see real fat loss results? Give it at least 4 months of consistent effort. It did not take you a month to gain the weight, and it won’t take a month to lose it either. Most research shows that sustainable fat loss happens at a rate of about 0.25 to 0.5 kg per week.
Should I stop fasting if I’m gaining weight? Not necessarily. Fasting is a tool. If it helps you eat fewer total calories, keep doing it. If it makes you overeat during your eating window, switch to a normal eating pattern with 3 to 4 meals per day. Research shows that when calories and protein are matched, fasting has no special fat burning advantage over regular eating.
Is it possible to gain muscle and lose fat at the same time? Yes, especially if you’re new to strength training, returning after a break, or carrying extra body fat. This is called body recomposition. The scale might not move, but your body shape will change. Measure your waist, track your strength in the gym, and take progress photos instead of relying only on the scale.
How many calories should I eat to lose fat? Take your body weight in kilograms and multiply by 26 to 28. That gives you a rough starting point for a moderate calorie deficit. Track your weight for 2 weeks. If you’re not losing about 0.25 to 0.5 kg per week, reduce by another 200 calories.
Do I need cardio to lose fat? No. Cardio burns calories, but diet does most of the work. A 2015 meta analysis found no significant difference in fat loss from meal frequency alone, and evidence shows that dieting produces meaningful weight loss while exercise alone often does not. The combination of diet and exercise gives the best results, but if you had to pick one, focus on your nutrition first.
Why is my belly the last place to lose fat? Belly fat, especially the deeper visceral fat around your organs, is influenced by genetics, stress, sleep, and diet quality. A 2014 study found that people who ate more saturated fat gained double the visceral belly fat compared to those who ate unsaturated fats, even with the same total calories. Reduce saturated fat, increase protein, manage stress, and be patient. Belly fat is usually the last to go and the first to come back.
How much water should I drink? Research shows that increasing water intake can reduce weight by boosting thermogenesis, reducing food intake, and increasing fat burning. There is a significant link between not drinking enough water and obesity. Aim for at least 2 to 3 litres per day, more if you exercise heavily or live in a hot climate.
Can supplements help me lose weight faster? Most weight loss supplements have no solid evidence behind them. Herbal products have not been shown to be effective for weight loss. Focus on protein intake, sleep, stress management, and a calorie deficit. These are the things that actually move the needle, and they cost nothing except discipline.
Before changing your approach, consider whether working out three times a week is enough for your goals. If you’re ready to commit to a transformation, find out whether you can get ripped in three months. A coach at one of the best gyms in Melbourne CBD can troubleshoot your plateau.
