Why Do We All Gain Weight Once We Start Working?

I remember that when I graduated from college, my weight held steady around 75 kg. Now, almost four years after graduating, I've gone from 75 kg to 80 kg, and at one point I even hit 85 kg.

In the second half of last year I decided to cut, and only then did I get back down to 75 kg. But that's a very hard weight to hold. As soon as my exercise or diet slips a little, it bounces right back to 80 kg.

This morning I watched a video by the Bilibili creator Xiaotoumingming, filmed during Bilibili's Top 100 Creators awards. They took photos of lots of creators from ten years ago and interviewed them, asking what had changed over the decade.

Maybe because they were comparing with photos from ten years ago, most of them, including Shi Pin Dao, Yu Ge Dao Chu Pao and Xiao Pianpian Shuo Dapian, said they'd gotten fatter and wider.

That made me wonder why so many people gain weight between their twenties and thirties.

Then, looking at my own numbers, I realized it's honestly a little scary when you think it through.

By mid-2026 I'll have officially been out of school for four years. If I hadn't deliberately controlled my weight last year, I'd have gained 5 kg over those four years.

And that's with me exercising, not a lot but consistently. If I didn't exercise and didn't manage my weight on purpose, I think I'd have gained well over 5 kg by now.

In 2023, Professor Mu Yiming of the Chinese PLA General Hospital published a paper called "Prevalence of obesity and associated complications in China: A cross-sectional, real-world study in 15.8 million adults," drawing on checkup data from 15.8 million adults.

The study found that obesity among Chinese men peaks at ages 35 to 39. In other words, from ages 20 to 35, men's weight is climbing fast.

The overweight rate among men reached 41.1%, and the obesity rate 18.2%.

So why does our weight keep climbing during these years?

When I think about it, my weight wasn't high back in college. Part of that is that I was young (I'm still young, of course) and my metabolism was high. The other part is that life on campus is very regular. Sleep, three meals and exercise all follow a steady rhythm, which is why my weight stayed so good.

After leaving campus for work, apart from sleep, my diet and exercise have gone almost completely out of order. I rarely eat at three fixed times a day, and most of the time it drifts by an hour or two either way. As for exercise, it vanished for the first year or two, and only in the last couple of years have I started exercising now and then.

The medical journal The Lancet has repeatedly published pieces on obesity getting younger in modern society. They name two main reasons for the rapid rise in BMI among young people in China.

Sitting too much, and ultra-processed food.

I'd say I'm not someone who sits all day anymore. I travel for work a lot, and sometimes when I can't get a seat on the subway or bus, I stand. Sometimes I can't even get a seat ticket on the high-speed train, and I stand there too.

Once I spent eight months going to the office every day. Those were the eight months my lower back was under the most stress. It hurt every single day.

The back pain is only part of it. The important thing is that on a nine-to-five office day, you burn almost nothing, just like working in a factory. In school, at least there were forty-minute classes, changes of classroom and breaks between lessons. At work, you don't have to move at all. All the exercise I got in a day was the short walk to the station for the commute.

Eating is a problem too. Compared with school, I burn less, but I'm not eating less.

Ultra-processed foods are industrially made foods where you can barely see the original ingredients and lots of industrial additives have been used, like cola, milk tea, instant noodles, some ready-made meals, and puffed snacks such as potato chips. These foods are now part of young people's everyday diets.

They share one notable trait: very high in calories but not filling, and they spike your blood sugar fast, so you take in a huge number of calories without noticing.

For the past six months I've gradually been improving my eating habits, following a "two tight, one loose" strategy. I try to choose unprocessed or minimally processed foods for breakfast and dinner, and for lunch I eat ordinary home-style food, as much as I like within reason.

Why did I notice this in a creator's video? Because for the past six months I've been deliberately controlling my weight, so I'm sensitive to the topic.

My core purpose in controlling my weight is to avoid obesity. Obesity isn't a good thing. It is itself a chronic, whole-body inflammatory disease, and it affects the body in many ways.

The most common problems are probably fatty liver and the "three highs" (high blood pressure, high blood lipids and high blood sugar). Obese people face them early on, and the three highs plant the seeds for diabetes, cardiovascular disease and more.

For someone in their twenties like me, the scariest thing about obesity isn't that it looks bad. It's that it overdraws health reserves for the coming decades.

And as we all know, to escape obesity and lose weight, you have to rely on your body's own metabolism.

Metabolism slows with age. So the earlier you get a body that isn't obese, and the habit and awareness of controlling your weight, the better.

So I want to use the time while I'm still young to train more, and make my body as strong as I can.

Of course, reality always falls a bit short of the ideal. Instead of setting goals sky-high, you're better off grabbing every small chance.

Exercise as much as you can, eat healthily, and start from any tiny step.

References:

National Health Commission of the PRC. Report on the Nutrition and Chronic Disease Status of Chinese Residents (2020) [M]. Beijing: People's Medical Publishing House, 2021.

Chen K, Shen Z, Gu W, et al. Prevalence of obesity and associated complications in China:A cross-sectional, real-world study in 15.8 million adults[J]. Diabetes, Obesity and Metabolism, 2023, 25(11): 3390-3399.

Pan X F, Wang L, Pan A. Epidemiology and determinants of obesity in China[J]. The Lancet Diabetes & Endocrinology, 2021, 9(6): 373-392.

Monteiro C A, Cannon G, Levy R B, et al. Ultra-processed foods: what they are and how to identify them[J]. Public Health Nutrition, 2019, 22(5): 936-941.