Gaining weight comes down to consistently eating more calories than your body burns, but doing it in a way that builds muscle rather than just adding fat takes a bit more strategy. A healthy rate of gain is about 0.25% to 0.5% of your body weight per week. For a 175-pound man, that works out to roughly 0.4 to 0.8 pounds per week. For a 135-pound woman, about 0.3 to 0.6 pounds weekly.
Why You Might Be Underweight
Before changing your diet, it’s worth considering whether something medical is keeping your weight low. Several conditions can quietly burn through calories or block your body from absorbing nutrients properly. An overactive thyroid speeds up your metabolism. Celiac disease and chronic pancreas inflammation interfere with digestion. Undiagnosed diabetes can cause weight loss even when you’re eating enough. Depression, chronic stress, and anxiety all suppress appetite in ways that feel normal after a while.
If you’ve lost weight without trying, or you’ve always struggled to gain despite eating what feels like plenty, a basic checkup can rule out these issues. Gaining weight is much easier once the underlying problem is addressed.
How Many Extra Calories You Need
The core principle is a caloric surplus: taking in more energy than you use each day. Increasing your intake enough to gain one to two pounds per week is a reasonable target for most people, though leaning toward the slower end helps ensure more of that weight is muscle rather than fat. Gaining too quickly almost always means excess fat storage.
A practical starting point is adding 300 to 500 calories per day above what you currently eat. Track your weight weekly (not daily, since water fluctuations will mislead you) and adjust from there. If the scale isn’t moving after two weeks, add another 200 to 300 calories. Total overall caloric intake is the major driver of weight change, so the specifics of timing and meal composition matter less than simply hitting a higher number consistently.
What to Eat
Not all high-calorie foods are equal. You want calorie density paired with actual nutrition, not just empty energy. Some of the best options for packing in calories without needing to eat enormous volumes of food:
- Nuts and nut butters: almonds, walnuts, cashews, and natural peanut butter. A couple of tablespoons of peanut butter adds nearly 200 calories.
- Healthy oils: olive oil, avocado oil, and peanut oil. Drizzling a tablespoon of olive oil on a meal adds about 120 calories you’ll barely notice.
- Avocados: calorie-dense and full of heart-healthy fats.
- Fatty fish: salmon, tuna, sardines, and trout provide both calories and protein.
- Dried fruit: dates, raisins, prunes, and apricots concentrate the calories of fresh fruit into small, easy-to-snack-on portions.
- Seeds: sunflower seeds, chia seeds, flaxseed, and wheat germ blend easily into other foods.
Most of these are rich in unsaturated fats, which support heart health while adding the caloric density you need. Building meals around a protein source, a starchy carbohydrate like rice or potatoes, and one or two of these calorie-dense additions is a simple formula that scales up easily.
Protein for Muscle, Not Just Mass
Protein is the raw material your body uses to build muscle tissue. If you’re training (and you should be, more on that below), aim for 1.2 to 1.7 grams of protein per kilogram of body weight each day. For a 170-pound person, that’s roughly 93 to 131 grams daily. Spreading that across your meals tends to work better than trying to cram it all into one or two sittings.
Good protein sources that also add meaningful calories include eggs, chicken thighs, whole milk, Greek yogurt, salmon, and beef. If you’re vegetarian, lentils, chickpeas, tofu, and tempeh all do the job.
Eating More When Your Appetite Is Small
One of the biggest barriers to gaining weight is simply not feeling hungry enough. Two strategies help here: eating more frequently and drinking some of your calories.
Research published in the Journal of the American Heart Association found that eating more frequent, larger meals was associated with meaningful weight gain over time. Each additional medium-sized meal per day was linked to nearly 1 kilogram of extra weight gained per year. Small snacks, interestingly, had the opposite association. So if your goal is gaining, think in terms of full meals rather than grazing on handfuls of crackers throughout the day.
Liquid calories are especially useful when solid food feels like too much. A homemade smoothie with whole milk, a banana, a tablespoon of peanut butter, oats, and a handful of seeds can easily hit 500 to 700 calories and goes down much faster than a plate of food. You can add yogurt, honey, or ice cream to push the numbers higher. These are easier to manage when you genuinely can’t face a full meal, and the best part is you can adjust the flavor and ingredients to whatever you actually enjoy drinking.
Strength Training Makes the Difference
Eating more without exercising will add weight, but a large share of it will be fat. Resistance training signals your body to direct those extra calories toward building muscle. The difference in body composition between someone who gains weight with and without lifting is dramatic over a few months.
Two to three strength training sessions per week produces the most muscle size and strength. Start with two sessions spread a few days apart and add a third as you progress. Each workout should include one to two compound exercises (movements that work multiple joints at once, like squats, rows, or presses) for each major muscle group: chest, back, shoulders, arms, legs, and calves. That comes to roughly six to twelve exercises per session.
For each exercise, aim for two to three sets of six to twelve repetitions. The weight should be challenging enough that the last couple of reps feel genuinely difficult. If you can breeze through twelve reps without effort, the weight is too light to drive muscle growth.
How Long It Takes to See Results
At a steady gain of half a pound to one pound per week, you’ll notice visible changes in about four to six weeks. Clothes fitting differently is usually the first sign. The scale should trend upward on a weekly basis even if individual days fluctuate. Weigh yourself at the same time each week, ideally in the morning before eating, and track the weekly average rather than obsessing over any single number.
If you’re gaining faster than about one percent of your body weight per month, you’re likely adding more fat than necessary. Slow down slightly by trimming 100 to 200 calories. If you’re not gaining at all after two to three consistent weeks, your surplus isn’t large enough. The process is iterative: eat, measure, adjust, repeat.
Common Mistakes That Stall Progress
The most frequent problem is overestimating how much you’re actually eating. People trying to gain weight almost always think they eat more than they do. Tracking your food for even one week with a simple calorie-counting app often reveals a gap of several hundred calories between perception and reality.
Another common issue is relying on junk food for the surplus. Fast food and sugary snacks will certainly add calories, but they crowd out the protein, vitamins, and minerals your body needs to build healthy tissue. You’ll gain weight, but you won’t feel or look good doing it. Prioritize the calorie-dense whole foods listed above and treat processed options as occasional extras, not staples.
Skipping workouts or doing only cardio is the third pitfall. Running and cycling burn calories you need for growth, and they don’t provide the stimulus for muscle building. If you enjoy cardio, keep it moderate and make sure you’re eating enough to compensate for those burned calories on top of your surplus.