Coffee and butter is known as the "artifact" of weight loss.

Butter in coffee, a popular weight-loss trick in the United States, has become popular in the UK as a fashionable diet, the Daily Mail reported. Drinks labeled "buttered coffee" are sold in many stores, and a large group of avid "fans" use it as a substitute for a meal.

The idea of putting butter in coffee came from American Dave Asprey, who drank buttered tea in Xizang in China and was curious about how mountaineers use it to replenish their energy, so he further thought of putting butter in his coffee. The principle of weight loss is that if you don't eat enough sugar in your diet, the body will use fat as a "fuel" to generate energy. Dave Asprey believes that this high-fat, low-sugar diet can fight fatigue, prevent chronic diseases, and lose weight.

But not any butter, it needs to be a kind of "grass-fed", salt-free butter. Milk, which makes butter, is produced by cows that feed on pasture rather than grain. Grass-fed butter is also rich in cancer-fighting antioxidants, fatty acids and beta-carotene, which are good for the brain and immune system.

Planet Organic, which makes and sells natural products, says buttered coffee has been popular for more than a year and is still rising.

But the way to lose weight with butter in coffee has also attracted some questions, and some experts who advocate traditional ways to lose weight believe that too low sugar intake can cause headaches, muscle spasms and digestive problems.