Why Gaining Weight Can Be Better for Your Longevity

Jan 30, 2024

100 Year Athlete Book Club: ROAR, Chapter 5: Weighty Matters

Weight is one of the most misleading yet popular signals about health and performance. Many people have a number in their head about what they should weigh, and anything heavier is “bad.” 

The truth is, that number is probably arbitrary, and chasing it won’t help you look, feel, or perform better. The conflicting cultural signals we get about weight—from “love your body” to everyone should look like Barbie—don’t help either. 

As Dr. Stacy Sims advises in ROAR, Chapter 5: Weight Matters, we need to focus on optimizing for our body type and physiology. To make this as useful as possible, let’s distinguish between three common goals: Vanity, Longevity, and Performance.

For most women, Vanity is about looking “skinny” in a bathing suit and staying under an arbitrary weight. Longevity is about maximizing athleticism, health, and quality of life as we age. Performance is about doing a sport or activity at peak ability, usually for the sake of competition. Optimizing your weight for performance or vanity doesn’t necessarily support longevity. Let’s compare the underlying mindsets:





Muscle Mass

I’m afraid to look “too muscular,” so I’ll only do cardio and exercises that “tone” my body.

I add muscle mass to prevent injuries and optimize my overall health as I age. 

I must be as light as possible to win at my sport. I’ll sacrifice some muscle mass.


If I unexpectedly gain weight, I take drastic measures to get below my target again

I gain mass in the winter and lose it in the summer, following the body’s natural rhythm. 

I can’t be at peak performance weight all the time. If I try to be, there are consequences. 


I avoid carbohydrates and minimize calories, regardless of my activity level, to ensure I weigh less than a certain amount. 

I eat and fuel properly to prevent Relative Energy Deficiency in Sport (REDS), a serious condition that disrupts menstruation, hurts recovery, and leaves me feeling depleted.

While I might decrease or increase calories significantly, I do so only for a short timeframe to boost performance. 

Body Fat

I focus on weight, which has little to do with health. Why am I tired all the time?

12% to 22% body fat is ideal for athletic women. 16% to 25% is good for general fitness, and 18% to 30% is the range for good health. To test body fat, I get DEXA scans on the same machine at the same location. 

Depending on my sport, I may flirt with the minimum body fat range for good health—10% to 12%—or the upper end of good health—30%.   

As you probably guessed, the Vanity mentality is terrible for longevity. It causes people to look a certain way at the expense of their overall health and wellbeing. The Performance mentality can be healthy within reason. You can’t be at peak performance 100% of the time. It's just not feasible. It's not sustainable. And it's ultimately not good for your longevity. The Longevity mindset is sustainable and avoids the extremes of the other two mentalities while ensuring that you look good, feel good, and perform well. 

Based on Sims’ research, longevity for women starts with gaining muscle mass, which adds weight but makes it easier to lose body fat. It means eating a base of 180 to 200 grams of carbohydrates daily —women need more carbs than men. It means not fasting. While many men benefit from fasting and can train fasted, it is never, ever helpful for women to fast according to Sims. It also means optimizing for your body type, the next thing we’ll discuss.

There are three body types, and no one is just one type. If each is a point of a triangle, we’re all somewhere in the area between the points. Broadly, here are the differences and needs.

Ectomorph: You’re skinny and struggle to gain weight (and other women hate you for it).

  • Focus on strength and power in training. They are the hardest for you to develop. 
  • Eat good quality fats, 30-35 g protein every meal, with three to five meals a day. 
  • Do not restrict carbs. You need them for fuel and energy.

Mesomorph: You have an athletic build and generally can add or drop weight if you try.

  • Focus on moderate endurance training, high intensity interval training (HIIT), and plyometrics. 
  • Eat good quality fats and moderate amounts of carbs (but less than an ectomorph would). 
  • Get 30-40 g of protein per meal and 15 grams per snack.

Endomorph: You’re curvy and find it easier to gain weight than lose it.

  • Focus on strength training and HIIT.
  • Get carbs from a variety of veggies and fruits and some grains. Avoid starchy carbs like potatoes.
  • Eat your bodyweight in grams of protein to optimize body composition, insulin, and blood sugar control. 

The bottom line: Focus on body composition (lean mass v. body fat), not the scale. You’ll feel, look, and perform healthier at 140 pounds with more muscle and less fat than you will at 135 pounds with more fat and less muscle.