Contents 7 sections
What is your main goal?
How do you digest dairy?
What matters most to you?
Summarise this article with:
💡 The essentials
- Decathlon sells two mass gainers under its own brand: the Muscle Gainer oats and whey (36 g of protein per 100 g, $39.09 for 1.5 kg) and the Weight Gainer oats and whey (17 g of protein, $23.45 per kilo), read on decathlon.fr on 31 October 2026.
- To build muscle, the Muscle Gainer is the right pick: twice the protein, a quarter of the sugars, and about $72 per kilo of protein against $138 for the Weight Gainer.
- To simply add calories, Optimum Nutrition’s Serious Mass (also sold by Decathlon, $54.73 for 2.7 kg) is the cheapest per calorie, but it holds only 15 g of protein per 100 g.
- Our verdict: the Decathlon Muscle Gainer is a good gainer at a fair price, made in France. Nutripure’s Pure Gainer beats it in the 4 kg bucket, with less sugar.
Want to bulk up and shopping in Decathlon’s nutrition aisle? You will find dozens of mass gainers there, two of them under the Decathlon brand with almost identical names. Muscle Gainer or Weight Gainer, and is it really cheaper than elsewhere? We read the labels and the day’s prices to answer you, with the numbers.
🔬 Our method
This page is based on the product pages of decathlon.fr, optimumnutrition.com and nutripure.fr (ingredients, nutrition facts, euro prices), read on 31 October 2026. These shops bill in euros: dollar prices are converted at the European Central Bank rate of 30 October 2026 (1 € = $1.1172). We do not run lab tests and we do not taste the products: we compare labels, a price per kilo of protein and a price per 1,000 kcal, with the same grid as every brand on the site.
🛒 Which mass gainers does Decathlon sell?
The gainer aisle of decathlon.fr listed 223 products on 31 October 2026, but most come from third-party sellers on its marketplace (Mutant, Dymatize, BioTechUSA…). Sold and shipped by Decathlon, you mainly find its two in-house gainers and Optimum Nutrition’s Serious Mass. For the chain’s regular whey, read our Decathlon whey review.
Decathlon Muscle Gainer oats and whey, the highest in protein
| Criterion | Muscle Gainer oats and whey (chocolate) |
|---|---|
| Protein per 100 g | 36 g |
| Energy per 100 g | 375 kcal |
| Carbs per 100 g | 45 g, of which 8.6 g sugars |
| Main ingredients | Whey protein concentrate 42%, oat flour 27.1%, dehydrated wheat syrup 21%, chocolate powder |
| Made in | France, Grassfed-labelled whey |
| Price | $39.09 for 1.5 kg ($26.06 per kilo) |
| Price per kilo of protein | about $72 |
It is a “lean” gainer rather than a weight gainer: a 100 g serving in 250 ml of water brings 375 kcal and 36 g of protein, roughly one and a half servings of whey. The recipe is short, with no intense sweetener, and Decathlon says it is made in France at an IFS Food certified site. It is rated 4.6 out of 5 on decathlon.fr, on 268 reviews. The page also offers a monthly subscription at 10% off, which brings it to about $35.18.
Decathlon Weight Gainer oats and whey, the highest in calories
| Criterion | Weight Gainer oats and whey (chocolate) |
|---|---|
| Protein per 100 g | 17 g |
| Energy per 100 g | 380 kcal |
| Carbs per 100 g | 68 g, of which 30 g sugars |
| Main ingredients | Gluten-free oat flour 36%, dehydrated wheat syrup, beet sugar, whey protein concentrate 15%, chocolate powder 15% |
| Price | $23.45 per kilo |
| Price per kilo of protein | about $138 |
The Weight Gainer is first a way to eat more calories: a 125 g serving brings 475 kcal, 85 g of carbs and only 21 g of protein. Its weak point is sugar: 30 g per 100 g, or 38 g per serving, from beet sugar and wheat syrup. It is rated 4.6 out of 5 on 116 reviews, and its cocoa is Fairtrade certified.
Optimum Nutrition Serious Mass, sold by Decathlon
Serious Mass is the most caloric gainer in the aisle: 1,262 kcal and 50 g of protein in a 336 g serving, with 3 g of creatine. But per 100 g it holds only 15 g of protein, and its first ingredient is corn maltodextrin, with sucralose. Decathlon sells it at $54.73 for 2.7 kg (rated 4.6 out of 5, 216 reviews). Deal of the day: it costs $49.38 on Optimum Nutrition’s site, thanks to a 15% discount shown on 31 October 2026. For the brand, read our Optimum Nutrition review.
⚖️ Muscle Gainer or Weight Gainer: which one to choose?
| Criterion | Muscle Gainer | Weight Gainer | Serious Mass |
|---|---|---|---|
| Protein per 100 g | 36 g | 17 g | 15 g |
| Sugars per 100 g | 8.6 g | 30 g | 3.2 g |
| Energy per serving | 375 kcal (100 g) | 475 kcal (125 g) | 1,262 kcal (336 g) |
| Sweetener | None | None | Sucralose |
| Price per kilo | $26.06 | $23.45 | $20.27 |
| Price per kilo of protein | about $72 | about $138 | about $135 |
| Price per 1,000 kcal | about $6.95 | about $6.17 | about $5.38 |
If your goal is to build muscle, take the Muscle Gainer: it brings the most protein per dollar, with little sugar. If you are a true “hardgainer” who cannot eat enough, the Weight Gainer and Serious Mass bring cheaper calories, but mostly carbs. Before choosing, read our whey vs mass gainer comparison: many lifters do not need a gainer at all.
ℹ️ Good to know
A gainer does not build muscle on its own: the calorie surplus, the protein and the training do. If you already eat enough, a whey protein for bulking with a bowl of oat flakes does the same job, often for less.
💶 Decathlon gainer or Nutripure Pure Gainer?
| Criterion | Decathlon Muscle Gainer | Nutripure Pure Gainer (unflavoured) |
|---|---|---|
| Protein per 100 g | 36 g | 34 g, some of it collagen |
| Sugars per 100 g | 8.6 g | 3.4 g |
| Energy per 100 g | 375 kcal | 395 kcal |
| Carbs | Oats, wheat syrup, sugar from the chocolate | Micronised oat flour |
| Made in | France | France |
| Price on 31/10/2026 | $39.09 (1.5 kg) | $33.40 (1.2 kg) to $94.85 (4 kg) |
| Price per kilo of protein | about $72 | about $70 (4 kg) to $82 (1.2 kg) |
In small sizes, the Decathlon Muscle Gainer is cheaper: about $72 per kilo of protein, against $82 for Nutripure’s 1.2 kg pouch. We say so plainly. In the 4 kg bucket, the Pure Gainer comes first (about $70), with two and a half times less sugar thanks to oats without added syrup. Of its 28 g of protein per serving, 11 g come from collagen, a less complete protein than whey: keep that in mind when you compare grams. The Pure Gainer is our pick for a clean bulk, and the Muscle Gainer remains a very good buy in store.
⭐ Our rating of Decathlon gainers
| Criterion | Muscle Gainer | Weight Gainer |
|---|---|---|
| Price per kilo of protein | ★★★★☆ | ★★☆☆☆ |
| Protein content | ★★★★☆ | ★★☆☆☆ |
| Recipe (sugars, additives) | ★★★★☆ | ★★☆☆☆ |
| Transparency (factory, origin) | ★★★★☆ | ★★★☆☆ |
| Customer reviews | ★★★★☆ | ★★★★☆ |
✅ Who is it for? ❌ Who is it not for?
- For you if you want a protein-rich gainer without sweeteners, to buy in store or pick up the same day: the Muscle Gainer.
- For you if you have a very small appetite and above all need to add calories: the Weight Gainer, or Serious Mass on sale.
- Not for you if you gain fat easily: prefer a whey and a real snack, see our guide whey or mass gainer for bulking.
- Not for you if you are under 14, have kidney or liver disease, or are pregnant: Decathlon advises against its gainers in these cases.
🏁 Our verdict on the Decathlon mass gainer
The Muscle Gainer oats and whey is Decathlon’s good gainer: 36 g of protein per 100 g, little sugar, made in France and fairly priced. The Weight Gainer, too sugary and half as rich in protein, is only worth it if you are after calories first. And if you order online, Nutripure’s Pure Gainer in 4 kg remains our first choice for a bulk without excess sugar.
⚠️ Warning
A gainer supplements your meals, it does not replace them. Decathlon advises against it for under-14s, pregnant women and in case of kidney or liver failure, and recommends a doctor’s advice beyond two months of use. If you are allergic to milk or gluten, ask your doctor. To adjust your intake, read how many calories in whey protein.
❓ Frequently asked questions
What is the best Decathlon mass gainer?
The Muscle Gainer oats and whey: 36 g of protein and 8.6 g of sugars per 100 g, against 17 g and 30 g for the Weight Gainer. It works out at about $72 per kilo of protein.
What is the difference between the Decathlon Muscle Gainer and Weight Gainer?
The Muscle Gainer is rich in protein, the Weight Gainer in carbs. Decathlon sums it up on its page: the Weight Gainer has more calories and carbs and less protein, for weight gain.
Does the Decathlon mass gainer make you fat?
It makes you gain weight if you eat above your needs, like any gainer. With training, part of that surplus becomes muscle; without training, mostly fat.
How much does the Decathlon mass gainer cost?
$39.09 for 1.5 kg of Muscle Gainer and $23.45 per kilo of Weight Gainer, on decathlon.fr on 31 October 2026. Optimum Nutrition’s Serious Mass costs $54.73 for 2.7 kg there.
Where is the Decathlon Muscle Gainer made?
In France, according to the official page, at an IFS Food certified site, with Grassfed-labelled whey.
