Explainer · metabolism and thermogenesis after 35

Thermogenesis, Explained: What It Is — And What It Isn't

By OptiLife Editorial Team · Updated August 30, 2026

Why do people who eat carefully and stay active still see progress stall after 35?

The question

Most conversations about weight focus only on calories in, calories out. But metabolism is not a single dial — it is a set of processes that slows with age, and one of them, thermogenesis, is the part most people have never had explained. This explainer exists to help you understand it — and what a citrus-based supplement can and cannot promise about it.

What people used to think

That a slowing metabolism after 35 was simply about eating too much and moving too little — a math problem with a willpower solution.

How it works — the simple version

What the evidence says

Thermogenesis itself is established physiology. Separately, natural compounds — citrus extracts and green tea among them — have been reviewed as thermogenic agents. What the evidence does not say is that any specific branded product reproduces those results; ingredient research and product proof are different things.

A Reasonable Question

It is reasonable to be skeptical. There are plenty of wellness products online making claims that sound far more certain than the evidence supports.

That is why the useful question is not whether CitrusBurn sounds exciting. It is what the approach actually is, what evidence exists around it, and what you should realistically expect to learn before spending anything.