Why Did I Gain Weight After Starting to Exercise? 4 Reasons and When to Trust the Scale (and How to Track It in Suu)
Published: · Furkan Mert Fındıklı · 7 min read
Short answer: Weight gain in the first weeks after you start exercising is usually water, not fat: muscles store every gram of glycogen with at least 3 grams of water, and muscles repairing after unfamiliar exercise hold extra fluid for a while. Some people's appetite also creeps up. Look at a 3–4-week average before deciding anything. In Suu you see what you eat and what you burn on the same day.
You're training three times a week and watching what you eat, yet at the end of week two the scale shows a kilo more. It's one of the most common frustrations for beginners — and often the moment people quit.
The good news: early gain is rarely added fat. The scale weighs everything in your body — water, glycogen, gut contents — and starting to exercise changes all of them. Below are the four reasons, how to tell which one applies to you, and when you can trust the scale again.
Reason 1: your muscles store water along with glycogen
Muscles store energy as glycogen, and every gram of glycogen is stored with at least 3 grams of water.1 Once you train regularly, your muscles get used to using and refilling that store; the carbohydrate you eat after training refills it, and water comes along.
For example, if your muscles add 300 g of glycogen, that's roughly 1.2 kg on the scale: 300 g of glycogen plus at least 900 g of water. That weight isn't fat — it's a sign your muscles are adapting to training.
Drinking less won't prevent it. Even in an experiment where fluid was deliberately limited, muscles kept storing 3 grams of water per gram of glycogen; with enough water the ratio was higher still.1 Cut your water and it's you that goes short, not the scale.
Reason 2: repairing muscles hold fluid for a while
Unfamiliar exercise — especially movements that load the muscle while it lengthens, like downhill running, squats or slowly lowering a weight — causes micro-damage in muscle fibres. The repair that follows brings inflammation and swelling in the muscle; the soreness that lasts a few days is part of it.2
Repeat the same exercise and the muscle is damaged less — the repeated bout effect.2 That's why this reason is felt most in the first 1–2 weeks, or in weeks when you change your programme.
Reason 3: your appetite quietly goes up
In a 12-week supervised study, 35 overweight participants exercised five days a week. Average weight loss was, as predicted, 3.7 kg — but individuals varied widely: one lost 14.7 kg, another gained 1.7 kg. Those who lost less than predicted were eating about 268 kcal more per day and felt hungrier.3
Often this isn't deliberate: the post-workout “I earned it” snack, a smoothie, a sports drink. You only gain fat when you take in more energy than you use, as the NHS puts it.5 A practical rule: count only half of the calories a workout burns as “available to eat back”.
Reason 4: the scale moves every day, and muscle comes slowly
Daily weight shifts with water, salt, gut contents and the day of the week. A study of more than 4,600 weigh-ins from 80 adults found weight rising at the weekend and falling during the week; the researchers treated this as a normal rhythm, not weight gain.4
Building muscle is a slow process over weeks and months; a sudden jump in the first few weeks is usually water and glycogen rather than muscle. To read the scale properly:
- Weigh yourself under the same conditions: in the morning, after the toilet, before eating or drinking, on the same scale.
- Use a weekly average: weigh in a few times a week and average them; don't react to a single day's jump.
- Give it 3–4 weeks: it takes a few weeks for water and glycogen to settle.
- Write down your waist measurement too: once a month, at navel height. How your clothes fit and the weights you lift are good signals as well.
- Log what you eat: post-workout snacks and drinks included.
Where to track this in Suu
Menu names are exactly as they appear in the app:
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Log post-workout snacks too
Home → quick add → Add Food → microphone or text field
“A banana, a protein bar and half a litre of sports drink” is enough; calories and macros are calculated and the drinks count towards your fluid balance. 3 AI analyses a day on the free plan.
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See whether your appetite went up
Nutrition screen → Last 7 days (calories)
Put the week before you started training next to the weeks after; if your daily calories crept up, it shows here.
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Count workout calories realistically
Home → quick add → Add Exercise
GPS workouts show an estimate of calories burned; when you plan to eat some back, count half of it, not all.
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Don't cut water — track it
iPhone: You tab → Water → Suu Index
Android: Statistics → Suu IndexOn training days your water goal rises automatically; the Suu Index scores your daily hydration from 0 to 100.
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Watch progress, not just the scale
iPhone: You tab → Exercise → Distance Milestones · Badges
Android: The Badges screen and Milestones at the end of a workoutDistance from runs, walks and hikes adds up into milestones, so your progress stays visible in the weeks the scale is noisy.
GPS workouts, milestones and badges are free; text and voice meal analysis is 3 times a day on the free plan.
In short
Weight gain in the first weeks of training is usually water and glycogen — a sign your muscles are adapting, not a reason to stop.
Weigh yourself under the same conditions, use a weekly average, give it 3–4 weeks and log what you eat after workouts too. If your average is still rising after a month, the answer is most likely on your plate.
Frequently asked questions
Why did I gain weight after I started working out?
Early gain is usually water: muscles store at least 3 grams of water with every gram of glycogen, and repairing muscles hold extra fluid for a while. Some people also eat more. Look at a 3–4-week average before deciding anything.
How long does weight gain from starting exercise last?
It varies, but gain from water and glycogen usually settles within a few weeks. If your 3–4-week average is still climbing, the cause is most likely what you eat — log post-workout snacks too.
Is the weight I gained from exercise muscle or fat?
In the first weeks it's mostly water and glycogen. Muscle builds slowly, and fat only increases when you take in more energy than you use. Your waist measurement and how your clothes fit are better guides than the scale.
When should I weigh myself after exercising?
Not straight after a workout. Weigh yourself in the morning, after the toilet, before eating or drinking and on the same scale each time, then average a few weigh-ins per week.
Is it normal to be hungrier after I started exercising?
Normal and common. In one 12-week study, people who lost less weight than predicted were eating about 268 kcal more per day. Logging post-workout snacks and drinks is the easiest way to spot it.
Should I drink less water so the scale doesn't go up?
No. Even when water is restricted, muscles keep storing water with glycogen; cutting back only leaves you dehydrated and makes training harder.
References
- Fernández-Elías VE et al. — Relationship between muscle water and glycogen recovery after prolonged exercise in the heat in humans. Eur J Appl Physiol, 2015
- Clarkson PM, Hubal MJ — Exercise-induced muscle damage in humans. Am J Phys Med Rehabil, 2002
- King NA et al. — Individual variability following 12 weeks of supervised exercise: identification and characterization of compensation for exercise-induced weight loss. Int J Obes, 2008
- Orsama AL et al. — Weight rhythms: weight increases during weekends and decreases during weekdays. Obes Facts, 2014
- NHS — Understanding calories
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Suu is not intended for medical diagnosis or treatment. Consult a healthcare professional for health-related decisions.