Look, most of the internet is obsessed with the opposite problem. You can't scroll for two seconds without seeing a "transformation" video or a new hack to drop ten pounds. But for people searching for how to get fat, the struggle is just as real, and honestly, way more frustrating because there’s almost no good advice out there that isn't just "eat a burger."
It’s hard.
Being chronically underweight isn't just about "looking skinny." It’s about feeling cold all the time, having zero energy, and watching your hair thin out because your body is literally scavenging itself for fuel. You want to gain weight. Not just a little bit, but enough to feel like a person again.
The Science of Why You’re Still Thin
Let’s get one thing straight: your "fast metabolism" is probably real, but it’s not magic. Researchers like Dr. Guyenet, author of The Hungry Brain, have spent years looking at how our genetics dictate our "set point." Some people just have a homeostatic system that works overtime to keep them at a certain weight. If you overeat one day, your body subconsciously moves more—fidgeting, pacing, even standing more—to burn off those extra calories. Scientists call this Non-Exercise Activity Thermogenesis (NEAT).
If you’re trying to figure out how to get fat or at least reach a healthy BMI, you’re fighting against your own nervous system. It’s not just about willpower. It’s about biology.
Think about it this way. Your body is a furnace. Most people have a furnace that’s easy to overwhelm. Yours? Yours is an industrial-grade incinerator. To make progress, you have to realize that "eating until you're full" is exactly what has kept you thin your entire life. Fullness is a lie your brain tells you to keep you at your current weight.
Why "Dirty Bulking" is a Trap
You’ve probably been told to just hit the drive-thru every day. People say, "Oh, just eat pizza and milkshakes, you'll get fat in no time."
That’s a recipe for disaster.
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Yeah, you’ll gain weight, but you’ll feel like absolute garbage. When you flood your system with refined sugars and trans fats, you trigger massive systemic inflammation. You might get a "gut," but your arms and legs will stay like toothpicks, and you’ll likely develop insulin resistance. That’s how you end up "skinny fat," which is arguably the worst of both worlds. You want mass that serves you. You want a body that can actually carry the weight.
High-Density Nutrition: The Only Way Out
To actually figure out how to get fat in a way that doesn't ruin your bloodwork, you have to master caloric density. This is the "cheat code" for people with small appetites.
A giant salad is the enemy. Why? Because it’s mostly water and fiber. It fills your stomach up, triggers those "I'm done" hormones like leptin and PYY, and leaves you with maybe 200 calories. You need the opposite. You need foods that are tiny but packed with energy.
- Liquid Calories: This is non-negotiable. It is significantly easier to drink 800 calories than to chew them. If you make a shake with whole milk, two tablespoons of peanut butter, a cup of oats, and a scoop of protein powder, you’ve just downed nearly 1,000 calories. Your brain doesn't register liquid fullness the same way it does solid food.
- Fats are your best friend: Protein and carbs both have 4 calories per gram. Fats? They have 9. If you add a tablespoon of olive oil to your pasta, you won't even taste it, but you've added 120 calories. Do that three times a day. Boom. An extra 360 calories without feeling "fuller."
- The Power of Nuts: Walnuts, macadamias, and almonds. Keep a bag on you. Eat them like medicine. A handful is 200 calories. If you eat four handfuls throughout the day while you're working or gaming, you've hit your surplus.
Stop Moving So Much (Seriously)
This sounds like terrible health advice, but if you're trying to gain weight, you need to audit your movement. Are you a pacer? Do you take the stairs every single time? Do you go for long, steady-state cardio runs?
Stop.
Cardio is great for your heart, but it’s a calorie-burning machine. If you want to get bigger, you need to lift heavy things and then sit down. Strength training—specifically hypertrophy work—tells your body to use those extra calories to build muscle tissue rather than just storing a bit of adipose tissue or burning it off as heat.
The Mental Game of Forced Feeding
Let's be real: eating when you aren't hungry is a chore. It sucks.
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When you're trying to figure out how to get fat, the kitchen becomes your gym. You have to treat meals like reps. If you wait until you're "hungry" to eat, you've already lost the day. You have to eat on a schedule.
- Breakfast is mandatory. No more "just coffee." You need eggs, avocado, and toast before 9:00 AM.
- The "Plus One" Rule. Whatever you normally eat, add one thing. One extra slice of bread. One extra spoonful of rice. One more glass of milk.
- Eat before bed. A slow-digesting protein snack (like cottage cheese or a casein shake) right before sleep prevents your body from entering a catabolic state overnight.
Common Mistakes That Keep You Small
Most people fail because they are inconsistent. They eat 4,000 calories on Monday, feel bloated and gross on Tuesday, so they only eat 1,500. By the end of the week, their average daily intake is still at maintenance. You aren't gaining weight because your weekly average is too low.
Tracking is annoying, but you probably need to do it for two weeks just to see how much you’re actually eating. Use an app like Cronometer. You’ll probably find that you're eating way less than you thought. "I eat so much" is the most common lie thin people tell themselves.
Specific Foods to Stock Up On
Don't overthink this. Go to the store and buy these specific things. They are the staples of any weight gain journey.
Dried Fruits: These are calorie bombs. Fresh grapes are mostly water. Raisins? They’re sugar and calories. Dates are even better. Two or three Medjool dates are almost 200 calories.
Full-Fat Dairy: Stop buying 1% or skim milk. Buy the red cap. Buy the Greek yogurt that has 10% fat. Use real butter, not the spray stuff.
Red Meat: While chicken breast is great for weight loss, you want ribeye. You want the fat. You want the calories that come with a marbled steak.
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Rice and Potatoes: These are your easy carbs. They're easy to digest, which means you'll be hungry again sooner.
The Role of Supplements
Do you need "Mass Gainers"? Honestly, usually not. Most mass gainer powders are just cheap maltodextrin (sugar) and protein powder sold at a massive markup. You're better off making your own.
However, Creatine Monohydrate is a legitimate tool. It draws water into your muscle cells, which increases your weight almost immediately (mostly water weight) and helps with protein synthesis. It's one of the most researched supplements on the planet. 5 grams a day. Every day.
Actionable Steps for the Next 24 Hours
If you’re serious about how to get fat and actually keeping that weight on, start right now. Don't wait for Monday.
First, go to the grocery store. Buy a jar of natural peanut butter, a gallon of whole milk, and a bag of trail mix.
Second, calculate your TDEE (Total Daily Energy Expenditure) online. Whatever that number is, add 500 to it. That is your new "survival" number. If you don't hit that number, you didn't finish your job for the day.
Third, start a basic strength program. You don't need to be a bodybuilder, but you need to give those calories a reason to stay on your frame. Focus on compound movements: squats, deadlifts, and presses.
Consistency is the only thing that works. You didn't get thin overnight, and you won't get "fat" or "buff" overnight either. It’s a slow, sometimes uncomfortable process of pushing your body past its comfort zone. Eat when you don't want to. Drink the shake. Lift the weight. Stop pacing. In three months, you’ll look in the mirror and finally see a different person.