Do fat-burning foods like green tea, chili and celery actually work?

There is a real but small effect behind the headlines. Green tea is the most studied. Dulloo and colleagues showed in a controlled trial that an extract rich in catechins and caffeine raised 24-hour energy expenditure by about four percent. In a meta-analysis by Hursel and colleagues, catechins produced just over a kilo of lower body weight on average, with wide variation between studies and an effect that faded in habitual coffee drinkers. Chili points the same way. A meta-analysis by Zsiborás and colleagues found that capsaicin raised energy expenditure by roughly 59 kilocalories a day, but only in people with overweight and not at all in those of normal weight.

Put the numbers in context. 59 kilocalories is about a bite of bread, and earning them means genuinely eating hot food every day. Green tea's kilo followed weeks of high extract doses, not a few cups of tea. "Negative calories", the idea that celery or grapefruit costs more energy to digest than it contains, has no basis. The body spends at most around a fifth of a meal's energy on digestion, and for vegetables the share is smaller still. No food ends up in the red.

The point is not that tea or chili is bad. They simply hold no shortcut. Fat comes off when intake stays below expenditure over time.

The promise sells because it shifts the responsibility from how much you eat to what you eat. Adding a cup of tea is easier than eating less, and a product that "burns fat" feels like effort without sacrifice. The supplement and detox industry lives on exactly that feeling. A jar or a powder with a mechanistic claim can be priced high, while the advice to eat a little less cannot be sold at all. Single studies with statistically real but tiny effects also make marketing gold. "Raises metabolism" is true in the lab and misleading in the kitchen, and the gap between the two is precisely what the industry profits from blurring.

Drink green tea because you enjoy it and spice your food if you like it hot, but don't expect either to move the scale. Spend no budget on fat-burning foods or negative-calorie lists. What decides things is your energy balance over weeks. If you want to see how large a deficit your body actually needs to lose fat, work that out instead of chasing magic ingredients.