Diminishing returns as the numbers of scale increase.

The growth might seem impressive when you do percentages of a very small number, but it's still a very small number overall.

It's not though, that's my point. Even in absolute terms, weight gain from growth in the first year is still more than any other time in the average person's life.

Putting on 6kg in a year is not that fast, people do sometimes gain weight faster than that in adulthood.

That's not growth, just fat accumulation which is a much simpler process.

How are you defining growth? Are you defining it by volume? Ie assuming the body mass density remains the same, how much does the weight increase (which means the body is volumetrically growing)?

If not--I am very lightweight right now, and I'm trying to put on body mass by eating more and exercising. While my volume will increase, my main growth is in density. My growth is not in fat, but actual muscle mass. Is this growth? If so, I have gone from 125lb to 140lb in ~2 months, which in absolute terms is obviously more than the baby (my goal is 160lb by the end of the year).

A few years ago, I went from ~130lb to 165 lb in three months--blame the free food at FAANG cafes during an internship. But this might be closer to what you were saying earlier--putting on fat.

Edit. I guess in the original statement saying that a person will never gain weight at this rate again there should be the explicit assumption that we're talking about natural growth, not growth due to external factors (ie more eating--intentional or not). In that case, that statement would be true.

I wouldn't say that growth through eating is unnatural though.

I guess what I might have implied by "natural" is growth from growing older as opposed to growth from nutrition.

But in that sense, of course a baby will have more growth than an adult--isn't it reverse exponential?

And a child puts on 100% bone and muscle?

No, but I'm not sure what point you're trying to make?

I was just pointing out that a baby does not gain weight faster than it ever will again in its life, in absolute terms. That's all. Not sure why I got the downvotes and no-true-scotsman arguments in return.

Plus fat and some water, yes. And furthermore, to go from a 10 pound baby to a 100 pound adult, I will make the claim that a baby has to gain 900% body mass.

I'm going by average weight gain from normal growth. But let's look at height instead then.

Average height at age 12: 59". At age 13: 62". 3" of growth.

At birth: 19". At one year: 29". 11" of growth.

Try matching that just by eating more.

(obviously, yes, it's easier for a small thing to grow than a large thing. But it's still crazy fast. Imagine being 50% taller in a year)

You talked about weight gain, in absolute terms. A novice powerlifter can easily put on both more absolute weight and absolute strength in a year than a newborn.

The image of a baby trying to outlift the weights that a novice weightlifter is lifting is now ingrained in my mind.

What I was trying to say is the baby is growing faster. If you stay at average weight throughout your life, like you're tracking along the 50% line on the growth chart, then your fastest weight gain is in your first year. On average that's when you gain the most weight (even in absolute terms), despite the fact that you're much much smaller than, say, a growing teenager.

But putting on 100% or even 200% of weight in a year is not normal or even possible for most adults without crippling their health. All babies do this.

I believe the GP was contesting the "In absolute terms!" part of the comment.