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How to Gain Weight On a Keto Diet (Without Getting Fat)


Healthy weight loss is often the goal of keto. A high-fat ketogenic diet has been shown to reduce cravings, increase fat burning, and provoke metabolic changes that support this goal[*].


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But what if your goal isn’t to lose weight? What if your goal is to gain weight?

Being underweight, it’s true, is linked to some unfortunate health consequences. On the other hand, adding muscle has many benefits. It can be desirable to add lean mass in a healthy way.

Got you covered. Learn the problems with being underweight, how to gain weight on keto, the best keto foods for healthy weight gain, building muscle on keto, and more.

What Does Underweight Really Mean?

The term “underweight” refers to a body mass index (BMI) of under 18.5. (BMI is weight in kilograms divided by height in meters squared.) Use this NIH calculator to determine your BMI.

Here’s a handy BMI reference table:

  • Underweight: less than 18.5
  • Normal weight: 18.5-24.9
  • Overweight: 25-29.9
  • Obese: Over 30

As of 2010, about 1.7% of US adults over 20 (2.4% of women and 1% of men) were underweight, according to the above BMI metrics[*].

Health problems linked to being underweight

Being skinny isn’t always desirable. There are, in fact, health consequences linked to having a low BMI.

For instance, a Swedish population study found that being underweight more than doubled the risk for all-cause mortality. Being obese only raised the risk by 50%[*].

Another group of researchers followed 48,287 Dutch people for six years, looking for a link between BMI and mortality. Results? Increased risk of death for underweight and obese men, but not for underweight and obese women[*].

Scientists have also studied cardiovascular disease (CVD) risk as it relates to BMI. In one study, researchers following 491,733 US adults found that being underweight increased heart disease risk by 19.7%[*]. Being overweight or obese increased CVD risk by 50% and 96%, respectively.

Here are some other health problems linked to being underweight:

  • Decreased bone mineral density (osteoporosis)[*]
  • Increased risk of dementia (one study found that the higher the BMI, the lower the risk of dementia, all the way up to “very obese”)[*]
  • Higher risk for age-related muscle decline, or sarcopenia[*]

A final note on these studies. Being underweight is associated with poor health, but cause and effect are not clear. In other words, something else may be driving the underlying health issue — protein or micronutrient deficiency, for example — and being underweight is merely a byproduct of that deficiency.

Alternatively, there may be nothing wrong whatsoever. Having a low BMI isn’t necessarily a bad thing (BMI is not a perfect measure of body composition, anyway) — but it does put you into some higher risk brackets.

What causes someone to be underweight?

Being underweight is often, but not always, a sign of an underlying condition. The accompanying unwanted weight loss — specifically, muscle loss — is also known as cachexia.

Here are some possible causes of cachexia:

  • Cancer: Cancerous tumors steal energy, and chemotherapy treatments can also accelerate muscle wasting[*].
  • Malnutrition: Caused by poor diet or medical condition.
  • AIDS: AIDS wasting syndrome (muscle wasting) is common.
  • Celiac disease: Gluten autoimmune condition causing poor nutrient absorption in the small intestine.
  • Crohn’s disease: An autoimmune condition that impairs intestinal nutrient absorption.
  • Anorexia: Eating disorders like anorexia and bulimia often cause weight loss.
  • Type 1 diabetes: If untreated, a lack of insulin (the hallmark of type 1) can cause rapid weight loss.
  • Hyperthyroidism: Excess thyroid hormone kicks metabolism into overdrive.
  • Neuroticism: This personality trait is positively correlated with being underweight[*]
  • Infection: Can affect appetite and metabolism.

As you can see, there are many possible causes of unwanted weight loss. Because of this, gaining weight isn’t always an easy proposition.

Reasons to Gain Weight, Not Lose It

If you’re underweight, or suffering from cachexia, the reasons to gain weight are fairly clear. According to population data, gaining weight lowers your risk for all-cause mortality, CVD, osteoporosis, dementia, and sarcopenia.

But even if you don’t have an underlying health issue, you may still want to add mass. What kind of mass? Muscle mass, of course.

Maintaining a healthy body composition is one of the best things you can do for your health. Muscle mass, in fact, is positively correlated with longevity[*]. More lean mass, longer life.

Adding muscle brings other benefits too, including:

  • More functional strength
  • Higher metabolic rate (more calories burned at rest)
  • Less age-related muscle wasting
  • Better bone density[*]

And yes, muscle also makes you look better, stronger, fitter, and healthier.

How to Gain Weight on Keto

Gaining weight is all about eating a caloric surplus. The principle is simple: If you eat more calories than you burn, you’ll probably gain weight.

To gain weight safely and steadily, aim for a modest caloric surplus of 200-300 additional calories per day. Remove any guesswork by recording your daily caloric intake and weighing yourself each morning. If you’re losing weight, you’ll need to increase your calorie intake a bit. Caloric needs, of course, will vary greatly between individuals.

For gaining weight on keto, think fat and protein. 

The ketogenic diet is a high-fat low-carb diet of about 60% fat, 30% protein, and 10% carbs by calories. Keeping carbs low, which keeps the hormone insulin low, is crucial for burning fat and producing ketones[*]. Dried fruit and whole grains are out.

To gain weight and build muscle, lean towards protein intakes of about 1 gram protein per pound bodyweight[*]. You may want to go higher, depending on your size, gender, and activity level. (Large, highly-active men need the most protein).

Since keto is a low-carb diet, the rest of your calories must come from fatty acid. That means your high-calorie diet will be rich in coconut oil, butter, cream, milk, cheese, olive oil, avocados and other healthy fats. Fat is highly satiating, so depending on your physiology, you may need to eat beyond the “I’m full” signal to gain weight.

Lastly, even though you’re limiting carbs, don’t skimp on non-starchy vegetables. These nutrient-dense foods contain vitamins and minerals — like magnesium and folate — that are absolutely vital for growth and repair.

Meal Timing, Sleep, Stress, Caffeine, and Gut Health

If you’re squeezing more calories into your day, you’ll want to eat multiple daily meals and avoid extended intermittent fasting schedules. A 12-16 hour fast is compatible with muscle gain, but beyond that, you run the risk of caloric deficit and weight loss.

Here are some other factors important for gaining mass:

Sleep: You need plenty of deep, slow-wave sleep to release human growth hormone (HGH), which stimulates bone, muscle, and cartilage growth. Quality sleep also helps you produce testosterone — an anabolic, fat-burning hormone[*].

Stress: Stress is catabolic, meaning it breaks down muscle. Why? Because stress, due in part to the hormone cortisol, puts you in “fight or flight” mode, not “growth and repair” mode[*]. If you’re being chased by a hungry leopard, building muscle is not a priority. Catabolizing muscle for energy, however, may help you escape.

Caffeine and nicotine: Caffeine and nicotine are both stimulants that activate the stress response in your body. They turn on chemicals called catecholamines, also known as adrenaline, that fire up your metabolism[*]. Because of this, caffeine and nicotine are more suited for weight loss — not weight gain — goals.

Creatine: Creatine has been proven, in study after study, to be a safe and effective strength supplement[*]. Five grams of creatine monohydrate per day can help with muscle gain goals.

Gut health: Having a healthy gut helps you absorb nutrients from your food. You can eat all the food you want, but if you aren’t absorbing it, you won’t gain weight.


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6 Foods to Help You Gain Weight on Keto

Okay, time for the fun stuff. You want to gain weight on keto. What healthy foods should you eat?

#1: Eggs

The almighty egg was made for the keto diet: high-fat, moderate protein, low carb.

Egg protein has a high bioavailability in the human body, rivaled only by whey protein[*]. Eggs are also rich in choline, an essential nutrient for liver, heart, and muscle health[*].

Scramble, whip up an omelette, or hard boil eggs for the road. A large egg contains about 80 calories. Simply add three or four to achieve a caloric surplus.

#2: Whey protein

Of all the protein supplements, whey protein is perhaps the most effective for building muscle. Whey is a complete protein (all 9 essential amino acids), highly bioavailable, and highly digestible[*].

Whey helps you add muscle, in part, because it’s rich in leucine. Leucine tells your cells: okay, time to gather the building blocks and build muscle now!

There are many clinical trials on whey for muscle growth. One group of researchers put 70 older women on a strength-training program. One group took whey, the other placebo[*]. Results? The whey-supplemented women maintained more muscle mass — promising for those trying to prevent sarcopenia.

To supplement, just add 20-30 grams whey protein isolate to your smoothie, blend, and enjoy.

#3: Full fat dairy

There’s a reason bodybuilders drink whole milk. It helps them get jacked.

That’s right. Full fat milk, cheese, cream, and other dairy products are excellent keto foods for building muscle. Along with fat, dairy products contain the milk proteins whey and casein, both of which have well-researched growth-promoting properties[*]. (If you have to choose one, though, choose whey).

Finally, dairy is rich in calcium, an essential electrolyte for muscle contraction and the main mineral that forms your bones.

So Grandma was right. You should drink your milk.

#4: Nuts

For a keto-friendly snack, you can’t beat a handful of cashews, macadamias, almonds, walnuts, or pistachios. They’re high in fat, high in nutrients, and a treat for the tastebuds.

A quarter cup of almonds, for instance, contains 49% of your daily biotin, 40% of your daily vitamin E, and 26% of your daily copper[*]. You need copper — scant in the modern diet — to support healthy immune function. Most nuts are a good source. (Peanut butter doesn’t count, because peanuts are actually legumes).

For an even easier snack, grab a high-quality nut butter and spoon away. You’ll be at a calorie surplus in no time.

#5: Meat and fatty fish

Beef, pork, chicken, salmon, and sardines are whole food protein staples on the keto-diet. Meat is fairly hypoallergenic, so it’s great for those sensitive to whey or egg protein.

And yes, the complete protein from meat and fish comes complete with plenty of leucine for muscle growth. Eat up.

#6: Healthy oils and fats

If you want to gain weight on keto, fatty acids are your friends. The most efficient way to mainline fat calories is to eat calorie-dense natural fats and oils.

That means butter, coconut oil, MCT oil, olive oil, avocado oil, and palm oil should be mainstays in your keto pantry.

Get creative. Use an extra pat of butter for cooking, pour extra olive oil on your salad, add a dollop of coconut oil to your spinach. If you’re really pressed for time, take a few swigs of avocado oil, right from the bottle.

Building Muscle on a Keto Diet

Contrary to bodybuilding lore, you don’t need carbs to build muscle. That’s right. High levels of insulin — a product of high-carb diets — are not necessary for muscle growth.

This has been shown. One group of researchers, for instance, found that a low-carb keto diet was better for muscle growth than a high-carb Western diet[*]. Kind of debunks the carbs-for-muscles hypothesis, doesn’t it?

So no, you don’t need carbs to build muscle — but you do need protein. The amino acid leucine, found in any complete protein, promotes muscle protein synthesis with or without high levels of insulin[*].

Where does keto come in? Well, leucine also interacts with the ketone body beta-hydroxybutyrate (BHB) to create a muscle sparing effect. In other words, keto helps preserve muscle[*].

But you can’t just sit on the couch and build muscle. You need resistance training. More on that next.

So yes, you can build muscle on keto, assuming you eat enough protein and lift heavy things. 

Best Exercises to Gain Weight

To gain weight and add muscle, you needn’t spend three hours at the gym each day. Nope. Two or three 30-60 minute weight training sessions per week will do.

To maximize these sessions, focus on compound lifts that work multiple muscle groups.

These lifts include:

  • Squats
  • Deadlifts
  • Lunges
  • Pull ups
  • Bench press (or pushups)
  • Overhead press
  • Rows

To build size, your best bet is to go low-rep and high-weight. 5×5 (5 sets of 5 reps each) is a common mass-gain protocol.

As always, injury prevention should be your number one goal — so be sure to warm up, rest for several minutes between sets, and maintain proper form throughout the routine.

Finally, if heavy lifting doesn’t work for your body, you can also build muscle with bodyweight exercises. It just might take a little longer.

The Takeaway: Can You Gain Weight on Keto?

Gaining weight on keto isn’t so different from gaining weight on another diet. You simply eat a caloric surplus.

Why gain weight? Perhaps to prevent being underweight, a state linked to a constellation of health issues. Alternatively, you may simply want to add muscle, feel stronger, and look better.


Join 90k+ people who are losing weight with Keto Kickstart, our doctor-developed program designed to give you real weight loss results.

To add muscle (and not fat) on keto, be sure you’re eating plenty of protein and healthy fats — and avoiding carbs and junk food. Combine that with a regular strength training program and you’ll be off to the races.


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