Mass-Gainer Overnight Oats
A jar of creamy overnight oats built to put size on you gently — about 45 grams of protein and 720 honest calories. Make it tonight, eat it tomorrow, and start the day already well fed. Real food doing the job most powders pretend to.
Plate 01 / Finished
Most shop-bought mass gainers are, to be blunt, a tub of cheap maltodextrin and a pinch of protein for a silly price. I used them in my twenties because I didn’t know better, and they sat in my gut like cement. When I started actually understanding food, I worked out you can build the same thing — high calories, decent protein — out of oats, milk, peanut butter and a banana, for a fraction of the cost and a fraction of the bloat. This jar is the result, and I’ve made it more times than I can count.
The whole point is ease. You stir it together at night while you’re cleaning up after dinner, leave it in the fridge, and in the morning it’s ready — thick, creamy, no cooking, no thinking. About 720 honest calories and 45 grams of protein waiting for you before you’ve even opened your eyes properly. On a build, when getting enough food in is half the challenge, having breakfast already done is worth more than any supplement. It’s a quiet, sturdy workhorse of a meal.
I’m not going to promise you it’ll “transform” anything, because nothing in a jar does that — the work happens in the gym and over months, not mornings. What this does is make eating enough genuinely easy, and it does it with real food you can pronounce. Make a couple of jars on a Sunday and your bulking breakfasts are handled for half the week. No fuss, no powder-shaker rinse, just good oats waiting for you. I’ve got you on this one.
01Who it’s for & when to eat it
This is a make-ahead, high-protein breakfast that flexes to your goal. The oat-and-protein base stays the same; you move the peanut butter, the oats, and the toppings. Here’s how I steer it.
The default jar
Full oats, a generous spoon of peanut butter, protein, banana and crushed nuts. Calorie-dense and effortless — the jar I lean on hardest when I’m trying to put size on without skipping meals.
Lighten it
Drop the oats, swap peanut butter for powdered peanut, use skimmed milk and lean on the protein and berries. You keep the convenience and the protein for far fewer calories. See the variations below.
Steady fuel
A moderate oat portion with full protein and a sensible spoon of peanut butter. Balanced carbs, fats and protein to keep you full through the morning without overshooting the day.
Timing: a grab-and-go breakfast, built the night before — slow carbs to carry you to lunch and protein to start the day strong. It also works as a sturdy snack between meals when you’re chasing calories on a build.
02Ingredients
Makes 1 jar. Easy to batch — make four or five jars at once and your week’s breakfasts are sorted.
Servings 1 · adjust on the live recipe card- Rolled oats70 g · 3/4 cup
- Milk or plant milk200 ml · 3/4 cup
- Greek yoghurt100 g · 3.5 oz
- Whey protein vanilla30 g · 1 scoop
- Peanut butter20 g · 1 tbsp
- Banana, mashed + sliced1 medium
- Chia seeds1 tbsp · 12 g
- Honey optional1 tsp · 7 g
- Crushed nuts to top15 g · 1/2 oz
- Cinnamon & pinch of saltto taste
Swaps I actually use: for a cut, swap peanut butter for powdered peanut, use skimmed milk and fat-free yoghurt, and drop the nuts. No whey? Casein makes it even thicker overnight, or use a plant protein. The chia is optional but it thickens the jar lovely and adds a little fibre and fat. Berries instead of banana lower the sugar.
03Step by step
Milk, yoghurt, protein into the jar
In a jar or tub, stir the milk, Greek yoghurt and protein powder together until smooth. Get the protein fully dissolved now — it’s far easier while it’s loose than once the oats go in and thicken it up.
Magnus says: a fork beats a spoon for breaking up protein lumps. Beat it properly smooth first.
Mash half, slice half
Mash half the banana and stir it through the wet mix for natural sweetness and creaminess. Keep the other half sliced to layer in and top with — it stops the jar tasting one-note and gives you something to bite.
Oats, chia, cinnamon, salt
Add the oats, chia seeds, cinnamon and a pinch of salt and stir well so everything is evenly coated and submerged. The chia needs to be mixed through, not clumped, so it gels evenly as it sits overnight.
Peanut butter and honey through
Drop in the peanut butter and the honey if using, and swirl them through — they don’t need to fully blend, those ribbons of peanut butter are part of the pleasure. Give it one last gentle stir to bring it together.
Lid on, into the fridge
Seal the jar and refrigerate for at least 4 hours, ideally overnight. The oats and chia drink up the liquid and go thick and creamy while you sleep. No cooking, no effort — the fridge does all the work for you.
Magnus says: if it’s too thick in the morning, a splash of milk loosens it right back. Too thin? It wasn’t long enough — give it more time next batch.
Sliced banana, nuts, dig in
In the morning, give it a stir, top with the reserved banana slices and crushed nuts, and eat it cold straight from the jar. Already done, already counted — a proper bulking breakfast with zero morning effort.
04The spec sheet
Real numbers, calculated — not guessed. The recipe makes 1 jar, around 520g of finished oats with toppings. Here’s what the full jar and a flat 100g actually give you.
| Nutrient | Per serving | Per 100g |
|---|---|---|
| Energy | 720 kcal | 138 kcal |
| Protein | 45.0 g | 8.7 g |
| Carbohydrate | 82.0 g | 15.8 g |
| — of which sugars | 30.0 g | 5.8 g |
| Fat | 22.0 g | 4.2 g |
| — of which saturates | 5.0 g | 1.0 g |
| Fibre | 11.0 g | 2.1 g |
| Sodium | ~0.3 g | ~0.06 g |
Moderate, and very easy to eat — cold, creamy oats go down without a fight. On a build that’s exactly what you want from a breakfast that has to carry real calories.
A lifter’s metric. Strong for a make-ahead carb breakfast — the whey and Greek yoghurt together push a humble jar of oats into proper-meal territory.
- Calcium~400 mg · 31% DV
- Magnesium~160 mg · 38% DV
- Phosphorus~500 mg · 71% DV
- Potassium~950 mg · 20% DV
- Vitamin B12~1.5 µg · 63% DV
- Zinc~3.5 mg · 32% DV
Macros are calculated from standard food-composition data and will shift a little with your exact ingredients and brands. Micronutrient figures are estimates against general adult Daily Values. Numbers are for guidance, not medical advice — see our Nutrition Disclaimer.
05Bulk / Cut / TRT variations
One jar, three jobs. The oat-and-protein base holds; you move the peanut butter, the milk, and the toppings. Macros below are for a full serving (one jar built as described).
Build it up
90g oats, a heaped spoon of peanut butter, full protein, whole milk, banana, honey and a generous handful of crushed nuts. Effortless, calorie-dense morning fuel for a serious build.
The lean version
45g oats, powdered peanut instead of the spoonful, skimmed milk, fat-free yoghurt, berries instead of banana, no nuts. Keeps the protein and the convenience, drops the calories right down.
Steady & balanced
65g oats, a sensible spoon of peanut butter, full protein, banana and a few nuts. Balanced carbs, fats and protein to keep you full through the morning without tipping the day over.
06Meal prep & storage
Overnight oats are practically built for meal prep — the whole recipe is “make ahead.” Line up a few jars on a Sunday and your bulking breakfasts run themselves all week.
Made jars keep four days sealed. Add fresh banana and the nuts on the morning you eat each one so the toppings stay crisp and bright.
You can freeze them, though the texture softens. Thaw overnight in the fridge and stir well. Honestly, fresh jars through the week are the better move.
If a jar’s gone very thick after a few days, stir in a splash of milk to bring it back to a creamy, spoonable texture. No reheating needed — eat it cold.
My move: five jars on a Sunday night, fifteen minutes of work, and breakfast is handled till Friday. On a build, taking the morning decision off the table is one of the kindest things you can do for yourself.
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07Common questions
How is this better than a shop-bought mass gainer? +
It’s real food, far cheaper, and far easier on your gut. Most gainers are mostly cheap sugar with a little protein. This jar hits similar calories and a solid 45g of protein from oats, milk, yoghurt and peanut butter — things you can actually pronounce, and that fill you up instead of bloating you.
Can I eat it warm? +
You can — give it a short, gentle warm in the microwave with a splash of milk. But honestly the magic here is no cooking; it’s designed to be eaten cold and creamy straight from the fridge. If you want hot oats, my stovetop peanut-butter protein oats are the better recipe.
Why are my oats too thick / too runny? +
Too thick means the oats and chia drank all the liquid — just stir in a splash of milk. Too runny usually means not enough chill time or too much liquid; give it the full overnight, and next batch add a touch less milk or a little more chia to firm it up.
Can I leave out the chia seeds? +
Yes — the oats will thicken fine on their own, just a little less so. Chia adds a thicker, puddingy texture plus some fibre and good fat. If you skip it, you might reduce the milk slightly so the jar still sets thick overnight.
Is it fine to make several days ahead? +
Up to about four days, yes — that’s the whole appeal. Keep the jars sealed and add the fresh banana and nuts each morning rather than at the start, so the toppings don’t go soft or brown sitting in the fridge.
This breakfast lives inside a full week of meals.
These oats are one breakfast in my 7-day bulking plan — seven days of high-protein, calorie-dense meals with the macros counted and the grocery list written. You pick the goal; I do the maths.
See the bulking meal plan →
08Pairs well with
Magnus Olafsson
I’m Magnus — twenty years under the iron, from a cold gym in Stockholm to the classic-physique stage, and now mostly in my kitchen in a pink apron. I’ve cut for shows, bulked through winters, and I’ve been on TRT since I was thirty-five. I know what it takes to eat for the body you’re chasing, and I know it shouldn’t come with a side of shame.
Everything here is food I actually cook and macros I actually count. I don’t diagnose, I don’t promise, and I never make a number up. I just feed you well and tell you the truth.
Slim Diet Era shares recipes and general nutrition information. It is not medical or dietetic advice, and we do not provide guidance on obtaining or using any controlled substance. See our Medical Disclaimer and Nutrition Disclaimer.