Carbs: Do They Really Make You Fat?

01The basics

Carbohydrates are your body's preferred source of energy — your brain, your muscles, and practically every cell reach for them first in day-to-day life. Broadly speaking, there are complex carbohydrates (whole grains, legumes, vegetables) and simple carbohydrates or sugar (table sugar, sweets, sugary drinks).

And yet carbs have a fairly bad reputation for a lot of people — "low carb" gets equated with "healthier" or "leaner" pretty quickly. Here's the principle we work from: the dose makes the poison, not a blanket verdict on an entire food group. Time to look at what the evidence actually says.

02What the science says

How many carbs does a healthy adult need?

The DGE recommends that more than 50% of daily energy intake come from carbohydrates, as part of an overall diet mindful of fat intake. The exact percentage matters less than the source: the DGE explicitly recommends nutrient-dense carbohydrate sources like whole grains, vegetables, fruit, legumes, and potatoes — they also bring vitamins, minerals, fiber, and plant compounds that heavily processed, sugary foods don't offer.

Do carbs really make you fat?

Short answer: not by themselves. A meta-analysis of randomized trials comparing low-carbohydrate diets to low-fat (and therefore relatively higher-carb) diets in overweight adults found a modest advantage for the low-carb approach in the first 6–23 months (roughly 1.2–2.1 kg more weight loss). By 24 months, that difference was no longer detectable — both approaches led to comparable results long-term.

The deciding factor for weight change is your overall calorie balance, not the carbohydrate share by itself. People eating fewer carbs often end up eating fewer total calories — not because carbs are "bad," but because cutting out one food group tends to lower total intake.

Sugar vs. complex carbs — what's the actual difference?

This is where it gets more nuanced. Free (added) sugar should, per matching DGE and WHO guidance, stay under 10% of daily energy intake — at 2,000 kcal, that's roughly 50 g, or about 12 teaspoons. The reason: sugary foods like sweets, baked goods, and sugary drinks deliver a lot of calories with few nutrients, and contribute to tooth decay, among other things. Complex carbohydrates from whole grains, vegetables, and legumes, on the other hand, digest more slowly, keep blood sugar more stable, and come with fiber and micronutrients on top. So the source of your carbs matters more than the raw amount.

Carbs and exercise: your glycogen stores

Your body stores carbohydrates as glycogen in your muscles and liver — roughly 300 g in an untrained person, up to 600 g in a well-trained endurance athlete, plus liver stores, for a total of up to 750 g. That's roughly 2,000 kcal of stored energy. During intense endurance exercise, these stores last around 90 minutes; once they're depleted, you hit the dreaded "wall," with a sharp drop in performance. If you train regularly, your carbohydrate needs are clearly higher than someone who's mostly sedentary.

Athlete nutrition isn't the same as everyday nutrition with training sessions

This is a distinction worth making, because it often causes confusion: endurance athletes training specifically for performance build their diet heavily around the sport — not 100% around "as healthy as possible" in the everyday sense. Someone running, cycling, or swimming for hours takes in enormous amounts of calories and carbohydrates, some of it as fast-acting sugar. That's not a contradiction of mindful eating — it's simply necessary: normal, fiber-rich whole foods can barely cover that demand during an intense session, because solid food sits too heavy and digests too slowly.

Above a certain intensity — beyond the anaerobic threshold — the body relies increasingly on carbohydrates, because fat oxidation is too slow to keep up. At the same time, glycogen stores gradually empty out. For efforts lasting more than about 60 minutes, sports medicine therefore recommends taking in additional carbohydrates during the session itself — typically 30–90 g per hour, often as sports drinks, gels, or bars with fast-acting sugar. These products are easy to digest and easy to dose — exactly what matters during exercise.

The key distinction: this is sports nutrition for a specific performance situation — not a green light to eat just as much sugar day-to-day. Someone jogging for an hour three times a week has different needs than someone training for a marathon or an Ironman. For most recreational athletes, the regular, balanced diet described in this article is entirely sufficient — gels and sports drinks only become genuinely relevant for longer, more intense sessions.

Even ordinary training benefits from the right preparation

That doesn't mean any of this only matters for competitive athletes. Even with a completely ordinary training routine — running three times a week, strength training, a weekend bike ride — your meal plan can be deliberately built around it: enough carbohydrates beforehand so your glycogen stores are well filled and you can actually train at the intensity you're aiming for, and the right intake afterward so your body can recover and the actual adaptation — supercompensation — can happen.

Exactly what that looks like in practice — how much, when, which foods — depends heavily on the individual: training volume, goals, tolerance, daily life, and preferences. There's no blanket rule here, just a good individual assessment. That's exactly what we're here for at ASCENSUS.

03How to put it into practice

1. Favor complex carbs: whole-grain bread over white flour, brown rice over white rice, legumes as a regular side — this gets you more nutrients per calorie.
2. Keep an eye on sugar, don't demonize it: an occasional slice of cake isn't a problem — around 50 g of free sugar a day is a rough ceiling, not a target.
3. Match the amount to your activity level: if you train, you can and should eat more carbs than someone who moves very little — especially around workouts.
4. Don't cut them out entirely: radical restriction usually backfires into cravings and rarely holds up long-term — the amount matters, not a blanket ban.