Illustration of a skinny guy who's worried about diabetes and insulin resistance while bulking up.

Can Bulking Cause Insulin Resistance & Diabetes?

Whenever we talk about how carbohydrates can be good for building muscle, we get comments from people worried that if they eat too many carbs, they’ll produce too much insulin, and their bodies will become desensitized to it, causing insulin resistance and potentially even leading to diabetes. Can that happen?

The other concern is that bulking means eating in a calorie surplus to gain weight intentionally. Can that calorie surplus cause insulin resistance?

I reached out to Dr. Karl Nadolsky, an endocrinologist who specializes in diseases like diabetes, and Danny Lennon, a nutritionist on the Advisory Board of the Sports Nutrition Association. I asked them if skinny and skinny-fat people should worry about eating too many carbs while bulking. Could that lead to insulin resistance and diabetes?

Their answers surprised me.

Before and after illustration of a guy recomping to burn fat and build muscle. Illustrated by Shane Duquette for Outlift.

Disclaimer & Introduction

This is a site focused on muscle and fitness. Marco has a degree in health sciences (BHSc) and is a certified nutrition coach. Cassandra is a registered nutritionist. However, I’m always hesitant to venture outside of our specific area of expertise. That’s usually when people start giving bad information.

However, we routinely get questions about how carbs, bulking diets, and bulking up affect insulin resistance and diabetes risk. So, we reached out to the relevant experts: Dr. Karl Nadolsky, an endocrinologist, and Danny Lennon, a nutritionist on the Advisory Board of the Sports Nutrition Association. They’re qualified to speak about how exercise and nutrition affect our likelihood of developing insulin resistance and diabetes.

The Basics of Insulin Resistance

What Does Insulin Do?

To understand how bulking affects insulin, we first need to understand insulin:

  1. When you eat carbohydrates, you break them down into simple sugars, which are released into your bloodstream.
  2. When your pancreas detects rising blood sugar levels, it secretes insulin, which helps that sugar enter your cells, where you can use it for energy or store it as glycogen.
  3. When your blood sugar drops back to normal, your pancreas stops producing insulin, and everything is back at baseline.

That’s how insulin is supposed to work. But when someone has insulin resistance, their insulin stops working as efficiently, forcing them to produce more of it to get the job done. The ominous thing is, if it continues getting worse, it can eventually lead to type 2 diabetes, usually after around 10 years.

What Causes Insulin Resistance?

The next question is, what causes insulin resistance? The two main drivers seem to be inactivity and excess body fat, both of which can cause fat to accumulate in the pancreas and liver, interfering with insulin production and signalling (study, study).

That’s where the fear of carbohydrates comes in. When you eat more carbs, you release more sugar into your bloodstream, causing your pancreas to secrete more insulin. If your pancreas or liver isn’t working properly, that can cause issues.

How Carbs Affect Diabetes Risk

Imagine you have a broken leg. If you walk on that broken leg, it could make your injury worse, so it makes sense to take a break from walking on it. But if you don’t have a broken leg, then you don’t need to avoid walking on it. In fact, that would do more harm than good. You’d miss out on all the health benefits of walking.

Carbs aren’t so different. If you don’t have insulin resistance, there’s no reason to avoid carbs, allowing you to take advantage of the many health benefits of fruits, vegetables, whole grains, and legumes. This will also pump your muscles full of glycogen, making them bigger and fuller, improving your performance in the gym, and speeding up muscle growth (full explanation).

Even if you do have insulin resistance, the only known way to reverse it is to attack the root of the problem—to get rid of the extra fat impairing your pancreas and liver. To do that, you can use a combination of a calorie deficit, hypertrophy training, and, ideally, some cardio:

  • The calorie deficit will help you lose weight.
  • The resistance training will encourage muscle growth, ensuring that the weight you lose is pure fat. Resistance training also burns through glycogen, allowing you to benefit from a higher carb intake.
  • People who do more exercise also tend to have proportionally less fat in their organs, even at the same overall body fat percentage.

Once you get the fat out of your organs, your pancreas and liver should begin working properly again, which will often get rid of insulin resistance. Or at least that’s my understanding of the situation. This is outside our area of expertise. So, I spoke with two experts: an endocrinologist and a nutritionist.

The Impact of Genetics & Age

The first expert I spoke with was Dr. Karl Nadolsky, an endocrinologist who specializes in diseases like diabetes. He’s also a fan of hypertrophy training, knows what bulking is, and understands how all of these pieces fit together.

He confirmed that eating carbs doesn’t cause insulin resistance. Rather, the two leading causes of insulin resistance are physical inactivity and high body fat levels. But he also pointed out that age and genetics can be factors, too. 

So if someone is in their sixties, they’re skinny-fat, and diabetes runs in their family, they might want to focus more on lifting weights, doing cardio, and eating a nutritious diet, less on bulking up.

For the rest of us, we aren’t at particularly high risk to begin with, and lifting weights and building muscle will only drop our risks even further. Bulking tends to be good for us.

Before and after photo of a man bulking up at 60 years old.

How Diet Affects Insulin Resistance

Next, I spoke with a nutritionist, Danny Lennon, a member of the Advisory Board of the Sports Nutrition Association. I knew about him because he hosts the Sigma Nutrition Podcast, which is widely regarded as being the most evidence-based nutrition podcast.

Danny told me that bulking up isn’t a problem, that lifting weights reduces our risk of developing insulin resistance, and that gaining muscle helps even more.

But, like Dr. Nadolsky, he pointed out that certain diets are better than others. He was more specific, too.

How Saturated Fat Affects Liver Fat

Danny Lennon told me that overconsuming saturated fat can cause extra fat storage in our organs, which can then contribute to insulin resistance, even when calorie intake is matched (study). For example, in a study by Bjermo and colleagues, the group given extra saturated fat increased their liver fat by 7%, whereas the group given extra polyunsaturated fat decreased their liver fat by 9% (study).

Graph showing how eating a bulking diet that's rich in saturated fat could lead to insulin resistance and diabetes.

That surprised me. I knew saturated fat could affect our blood lipids, but I didn’t realize it was tied to insulin resistance, too. It even seems to negatively impact insulin sensitivity when there aren’t any measurable changes in visceral fat (study).

How Soluble Fibre Affects Insulin Resistance

On the bright side, there are also foods that seem to help. In particular, soluble fibre. It can bind to the saturated fat you eat and carry it through your digestive system, reducing the saturated fat in your blood. That’s the type of fibre found in foods like:

  • Oats
  • Peas
  • Beans
  • Lentils
  • Chickpeas
  • Apples
  • Citrus Fruits
  • Carrots
  • Psyllium husk
Illustration of a muscular weight lifter drinking a bulking smoothie to build muscle and lose fat.

How Sugar Affects Diabetes Risk

Excessive consumption of refined sugar is associated with insulin resistance. It’s not quite the same as saturated fat, though, and the difference is important.

Sugary foods and sodas taste good and aren’t very filling, so people who eat more sugar tend to eat more food and gain more weight. And if they’re sedentary, more of that weight is stored as fat, and more of that fat winds up in their organs.

If the refined sugar you eat isn’t making you fat, there’s less of a reason to worry. If you’re lean, there doesn’t seem to be a direct link between sugar consumption and insulin sensitivity (though this is debated). Still, most guidelines recommend limiting refined sugar to less than 10% of your total calories. I think that’s wise.

Can Skinny Guys Get Insulin Resistance?

Skinny people are at low risk of getting insulin resistance because we have relatively low levels of body fat. As a result, we’re less likely to have fat in our organs, and so we’re less likely to have issues with insulin production and signalling.

On the other hand, we also have low amounts of muscle mass. Some of us also lead sedentary lifestyles. So, if we lift weights, bulk up, and gain muscle mass, our risk will drop even lower.

Let’s talk about why.

Big Muscles Reduce the Risk of Insulin Resistance

One of the ways insulin can carry sugar out of our blood is by converting it into glycogen and storing it in our muscles. When we build bigger muscles, our muscles are able to store more glycogen, giving us a greater reservoir to store extra sugar, which is great for our health and performance.

Illustration of a bodybuilder doing the dumbbell curl exercise to build bigger biceps.

Weight Training Reduces the Risk of Insulin Resistance

Lifting weights reduces all-cause mortality and helps prevent insulin resistance (study). There are a couple of reasons for that. First, lifting weights is a form of exercise, and exercise causes us to store less of our fat viscerally—to store less of our fat in and around our organs. And so, like other forms of exercise, lifting weights reduces our risk of developing insulin resistance.

Second, when we lift weights, we burn through the glycogen in our muscles, allowing us to fill them back up with the sugar in our blood. Our muscles are reservoirs. Lifting weights drains those reservoirs, allowing us to fill them back up again. This is especially true when people do more reps per set and more sets per workout, burning through more glycogen. That makes hypertrophy training (aka bodybuilding) especially helpful.

Illustration showing a man doing push-ups to build bigger shoulders.

What Body-Fat Percentage Puts You At Risk?

According to the National Institutes of Health, your risk of developing insulin resistance and diabetes only becomes significant once your waist circumference at belly button height creeps past 40 inches as a man or 35 inches as a woman (study).

If your waist is encroaching on 40 inches, I recommend cutting instead of bulking. Eat a good diet, lift weights, do some cardio, and try to get enough sleep, all of which will help you burn proportionally more visceral fat. When your waist circumference drops below 36 inches, you can start emphasizing muscle growth.

Summary & Guidelines

Here’s what you need to know about how bulking influences insulin resistance and diabetes risk:

  • The main drivers of insulin resistance are excess body fat and sedentariness, both of which cause visceral fat storage.
  • Carbs don’t appear to cause diabetes. You can eat a high-carb bulking diet without fear of it causing problems. Even better if your diet is rich in fruits, vegetables, whole grains, nuts, seeds, and legumes, all of which are rich in fibre, driving your risk even lower.
  • Saturated fat is linked with diabetes. Diets higher in saturated fat cause more visceral fat storage. We recommend bulking on a diet lower in saturated fat.
  • Building muscle reduces your risk. Bigger muscles soak up more sugar, making it easier to manage blood sugar levels.
  • Lifting weights reduces your risk. It burns through sugar, allowing you to benefit from eating more carbs.
  • Living a healthy lifestyle reduces your risk. Doing cardio, lifting weights, going on walks, and being active all reduce your risk of developing insulin resistance. So does eating a balanced and nutritious diet that’s rich in fibre.

Overall, bulking should reduce your risk of developing diabetes, provided you do it properly. You’ll be lifting weights, increasing your activity levels, eating more nutritious foods, and building more muscle, all of which should reduce your risk.

We’ve spent over a decade helping 15,000 members bulk up. Most of them get 40–60% of their calories from carbohydrates. We’ve never heard of any of them—not even one—developing insulin resistance or diabetes while bulking.

Cover illustration of the Outlift intermediate bulking program for naturally skinny guys.

Alright, that’s it for now. If you want more muscle-building information, we have a free muscle-building newsletter. If you want a customizable hypertrophy training program (and full guide), check out our Outlift Intermediate Bulking Program. Or, if you’re still new to bulking, try our Bony to Beastly (men’s) program or Bony to Bombshell (women’s) program. If you liked this article, I think you’d love our full programs.

Shane Duquette is the co-founder and creative lead of Outlift, Bony to Beastly, and Bony to Bombshell, and has a degree in design from York University in Toronto, Canada. He's personally gained 65 pounds at 11% body fat and has ten years of experience helping over 10,000 skinny people bulk up.

Marco Walker-Ng is the co-founder and strength coach of Outlift, Bony to Beastly, and Bony to Bombshell, and is a certified trainer (PTS) with a Bachelor's degree in Health Sciences (BHSc) from the University of Ottawa. His specialty is helping people build muscle to improve their strength and general health, with clients including college, professional, and Olympic athletes.

Cassandra González Duquette is a certified nutritionist (CNP) who studied at the Institute of Holistic Nutrition in Toronto, Canada. She's personally gained 22 pounds, going from 97 up to 119 pounds.