So overall, the weight loss we see from these high-quality studies is very small, and mostly with no change in body composition.

The studies included people with different diseases, and most were from the Middle East or the Indian subcontinent. So we can’t be certain we would see this effect in people with other health profiles and in other countries. They were also conducted over different lengths of time, from two to six months.

The supplements were different, depending on the study. Some had the active ingredient extracted from cinnamon, others used cinnamon powder. Doses varied from 0.36 g to 10 g per day.

They also used the two different types of cinnamon—but none of the studies used cinnamon from the grocery store.

How Could Cinnamon Result in Small Amounts of Weight Loss?

There are several possible mechanisms.

It appears to allow blood glucose (sugar) to enter the body’s cells more quickly. This lowers blood glucose levels and can make insulin work more effectively.

It also seems to improve the way we break down fat when we need it for energy.

Finally, it may make us feel fuller for longer by slowing down how quickly the food is released from our stomach into the small intestine.

What Are the Risks?

Cinnamon is generally regarded as safe when used as a spice in cooking and food.

However, in recent months the United States and Australia have issued health alerts about the level of lead and other heavy metals in some cinnamon preparations.

Lead enters as a contaminant during growth (from the environment) and in harvesting. In some cases, it has been suggested there may have been intentional contamination.

Some people can have side effects from cinnamon, including gastrointestinal pain and allergic reactions.

One of the active ingredients, coumarin, can be toxic for some people’s livers. This has prompted the European Food Authority to set a limit of 0.1 mg per kg of body weight.

Cassia cinnamon contains up to 1 percent of coumarin, and the Ceylon variety contains much less, 0.004 percent. So for people weighing above 60 kg, 2 teaspoons (6 g) of cassia cinnamon would bring them over the safe limit.