I Can't Gain Weight: What Science Says About Hardgainers

Because their body dissipates the excess. A study by the Mayo Clinic published in Science fed sixteen non-obese volunteers 1,000 kcal per day above their needs for eight weeks. Fat gain varied tenfold between individuals. Two-thirds of the increase in energy expenditure came from non-exercise activity thermogenesis, that is, spontaneous movements, posture maintenance, fidgeting, and variations in this expenditure explained storage differences with a correlation of 0.77. The authors conclude that faced with excess food, some people activate this expenditure and stay thin, others do not and store it.

Not in the sense of a higher resting metabolism: what varies most is expenditure related to spontaneous activity, not basal metabolism. The Science study measured that two-thirds of the increase in expenditure under overfeeding came from this non-exercise activity. A review in Current Obesity Reports specifies that during overfeeding, energy dissipation is explained solely by the adaptation of non-resting expenditure. The hardgainer therefore doesn't have an engine running faster at rest; he moves more without realizing it when he eats more.

In part. A study published in the New England Journal of Medicine overfed twelve pairs of identical twins by 1,000 kcal per day, six days a week, for 84 days, totaling 84,000 kcal excess. Average weight gain was 8.1 kg, but it ranged from 4.3 to 13.3 kg depending on the individual. The two twins from the same pair responded similarly, with three times more variance between pairs than within pairs for weight and fat mass, and six times more for fat distribution. The authors conclude that genetic factors govern the tendency to store energy as fat or lean tissue.

By accepting that the calculator underestimates your needs. If your body dissipates part of the surplus through spontaneous activity, a theoretical surplus of 300 kcal may show nothing on the scale. The method is empirical: start from the calculated surplus, weigh yourself weekly under the same conditions, and increase in increments of 200 to 300 kcal as long as weight doesn't go up, until you find the level where it rises slowly, around 0.25 to 0.5% of body weight per week. With resistance training and protein around 1.6 g per kilogram, so that this weight gain is muscle.

No, you need to eat slightly more than what your body dissipates, and that's different. Helms' trial shows that a very large surplus creates mostly fat, even in those who train. The hardgainer doesn't need to stuff himself; he needs to find, through successive trials, the surplus that makes his scale rise slowly. This surplus is often higher than for others, but it remains a moderate surplus once found. The hardgainer's problem isn't the theoretical quantity, it's the food volume needed to reach it when appetite doesn't follow.

By densifying rather than increasing volume. Calorically dense foods—nuts and seeds, olive oil, cheese, avocado, dried fruits—provide a lot in little volume. Liquids go where solids no longer do: a gainer or caloric smoothie provides 200 to 400 kcal without the volume of a meal. Eating more frequently, five or six meals instead of three, spreads the load. And drink between meals rather than during, to avoid filling your stomach with liquid before food.

It's precisely the profile for which it makes sense, as detailed in our gainer guide. The hardgainer has a calorie problem, not a protein one: he already eats, he trains, and the scale doesn't move because his body dissipates and his appetite plateaus. A liquid with 189 kcal and 12.6 g of protein goes where a fourth meal doesn't. It's dosed by the scale: one serving, then half a serving more if weight doesn't go up, counting its protein in your total.

If you've really eaten a lot for months, with honest tracking, and weight is dropping or stalled anyway; if thinness is accompanied by fatigue, digestive issues, diarrhea, abnormal stools, thirst or abundant urination, palpitations, sweating, or heat intolerance. An overactive thyroid, diabetes, celiac disease, or another malabsorption disorder explain some resistant cases of thinness, and they're detected by blood tests. A healthy hardgainer doesn't have these signs: he just has a stubborn scale.

That resistance to weight gain is real, measured in Science, and it works through spontaneous activity that dissipates the excess. That it's partly genetic, according to the twins in the NEJM. That the calculator therefore underestimates your needs and the scale alone tells the truth. That you need to increase in increments until slow gain, not stuff yourself. That volume is the real obstacle, and a caloric liquid bypasses it. And that signs associated with thinness warrant a doctor's visit.