Illustration of a lean man holding his stomach

If you’re a skinny guy who prides himself on having great ab definition, the idea of bulking up can be intimidating. The same is true for skinny-fat guys who have fought hard to lose fat and are now faced with the prospect of gaining it back.

Frankly, most people who bulk up do wind up gaining some fat. That’s not because they’re doing anything wrong, either. When gaining weight, you need to eat in a calorie surplus. And when you eat in a calorie surplus, there’s always the risk of some of those extra calories being stored as fat.

The good news is that as a naturally skinny guy—even if you’re naturally skinny-fat—you’ll probably have a small number of fat cells than the average overweight person. Because of this, ectomorphs tend to be a bit more resistant to gaining fat than the other male body types (study). If you bulk cleverly, you should be able to build muscle quite leanly.

There are also a few things you can do to reduce your risk of gaining fat while bulking:

  1. Follow the best bulking program you can find. The better your bulking workouts are, the more muscle growth they’ll stimulate, and so the more calories your muscles will soak up. It’s usually better to skip the bodyweight workouts and strength training programs, focusing instead of on bonafide bulking routines.
  2. Keep your calorie surplus relatively modest. With a good workout routine and a good bulking diet, most skinny guys are able to build muscle quite quickly and leanly during their first few months of training. During this period, we normally recommend gaining around a pound per week. However, if you’re worried about gaining fat, eat in a smaller surplus and gain weight more slowly. Gaining 0.5 pounds per week will give you a better shot of avoiding fat gain while bulking.
  3. Eat enough protein. Protein is the raw material that muscle is built out of. In order to build new muscle mass, we need to be consuming enough protein to build that muscle with. Unless you’re bulking on a vegan diet, getting enough protein from whole foods isn’t that difficult. If you’re finding it difficult, though, try getting a protein powder.
  4. Eat a higher carb diet for leaner gains. This one is surprisingly controversial, especially now that ketogenic diets are becoming more popular. However, keto isn’t designed for bulking, it’s designed for weight loss. The same is true with low-carb diets. Most guys are able to build muscle more leanly if they get up to around 50–60% of their calories from carbohydrates. (Having a little bit of sugar in your bulking diet is usually okay, too, provided that it’s not more than 10% of your total calorie intake.)
  5. Eat mostly whole foods for general health. Whole foods tend to contain more vitamins, minerals, phytonutrients, and dietary fibre. That’s going to help you build more muscle, and it’s going to help reduce the amount of fat you gain (study). Now, it’s true that foods that are higher in fibre are also more filling, which can make it hard for us skinny guys to eat enough calories. But there are ways to eat more calories while still eating a diet that’s healthy overall.
  6. Add in some cardio alongside your bulking workouts. If you’re new to exercising, lifting weights will probably improve your cardiovascular health. Even then, though, you’ll probably be able to build muscle a little bit more leanly if you add in a little bit of dedicated cardio to your bulking routine.
  7. Bulk up your abs. Most overweight people are naturally muscular in their abs and lower bodies. After all, they need to carry around their extra bodyweight with them everywhere they go. This gives their abs a ton of stimulation as they go about their everyday lives. This isn’t true for ectomorphs. Our lighter bodies don’t require as much core strength, so unless we train our abs directly, us skinny guys will often wind up with fairly skinny abs.

There’s more good news, too. Lifting weights will improve the insulin sensitivity in your muscle cells, making it more likely that the food you eat will go to muscle instead of fat (study). Plus, having more muscle mass on your body will further improve your insulin sensitivity, making it easier to be lean and muscular in the longer term (study, study).

There are tons of things that affect how lean your gains are—we’ve written an entire book about it. However, if you keep these principles in mind, you should do pretty well.


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