The researchers, affiliated with the Tehran University of Medical Sciences, looked at English language articles published up to March 2017 that have explored body measurement changes linked to popular weight loss ingredients green tea, caffeine, and capsaicin (the compound that give chilies their spiciness).
They looked at 29 placebo-controlled studies conducted on obese, adult humans, and found that green tea’s body of science has linked it to reduced weight, body mass index, and waist circumference. Capsaicin also had a “significant weight loss effect.”
Their report was published online ahead of print for the July 2018 volume of the Journal of Functional Foods.
Study design and definitions
Studies were collected from four databases: PubMed/Medline, Scopus, Cochrane Library, and Web of Science.
The researchers only included placebo-controlled clinical trials on adult humans. For green tea, they only included studies that used green tea extract as a whole instead of studies that isolated green tea’s catechins or polyphenols.
The outcomes they looked for comprised many different anthropometric changes—not just weight loss. This included weight gain, body composition changes, fat mass changes, changes in body mass index, and so forth.
Of the 29 studies they looked at, 20 of them were on the effect of green tea and green tea extract in either infusion or capsule form. Four studies looked at caffeine supplements, while five studies looked at capsaicin and red pepper supplements.
Some of the studies included had a physical activity component or a controlled diet during the intervention period.
Not enough data for caffeine
According to the researchers, their findings indicated that there is “significant weight loss after consumption of green tea, green tea extract and capsaicin [supplementation].”
Proposed mechanisms included green tea’s catechins decreasing pancreatic lipase activity causing lower intestinal fat absorption and higher fecal fat loss. For capsaicin, suggested mechanisms included increasing energy expenditure and fat oxidation in overweight and obese populations, and manipulation of gut microbiota.
Meanwhile, the body of science analyzed for caffeine did not show significant effects on anthropometric measures.
“There are few RCTs that assessed effect of caffeine on body weight and their results are conflicting,” they wrote.
Though there were studies supporting caffeine’s effect on physical performance and benefits on strength and power of muscles, there weren’t studies that specifically looked at changes in body weight or other measurements.
“Further RCTs is required to confirm the effect of caffeine supplements on weight,” they added.
Source: Journal of Functional Foods
Published online ahead of print, https://doi.org/10.1016/j.jff.2018.04.002
“Effect of green tea, caffeine and capsaicin supplements on the anthropometric indices: A meta-analysis of randomized clinical trials”
Authors: Mahdieh Golzarand, Karamollah Toolabi, Mohadeseh Aghasi