Green Tea for Weight Loss: Does It Work?

A long-trusted part of the diet

Green tea has a long track record as a beneficial part of the human diet. It's fairly well known for its antioxidant properties and its role in supporting immune function. It's also used to help lower the risk of certain cancers (skin, esophageal, stomach, colon) and to help guard against atherosclerosis, and it's a recognized source of fluoride for dental health.

The main biologically active compounds in green tea are bioflavonoids, caffeine (also called "theine" in tea), catechins, EGCG, flavonoids, fluorides, gallic acid, tannins, polyphenols, theophylline, and vitamin C. In a green tea extract specifically, there are two components worth paying attention to.

The first is caffeine. Caffeine constricts peripheral blood vessels while dilating those in the brain, which is why it acts as a mental stimulant but can actually worsen blood flow to muscle tissue. Caffeine used to be classified as a doping agent, but because it has little effect at low doses and tends to be counterproductive at high doses (it "throws you off" more than it helps), its use in sport is unreliable at best. Reduced blood flow to working muscle can increase injury risk in much the same way skipping a warm-up does. Excess mental stimulation can also impair muscular coordination with a similar result. In people prone to anxiety, repeated high intake can worsen their overall psychological state. Caffeine (theine) should be avoided during pregnancy, while breastfeeding, and by children. With regular use the body builds tolerance, and withdrawal can bring on headaches and sometimes low mood; higher doses become necessary over time to get the same effect.

The other key compound

The second component is EGCG — epigallocatechin gallate, a bioactive polyphenol found in green tea. It's been studied for a genuinely interesting range of effects.

EGCG has been linked to reduced mortality from cardiovascular disease (poor blood flow to the brain, heart, and other tissues). Its vasodilating effect (widening blood vessels) is thought to come from stimulating nitric oxide (NO) production from arginine. EGCG appears to slow the production of compounds that would otherwise inhibit nitric oxide synthase (NOS) — the enzyme responsible for converting arginine into nitric oxide. The main compound that inhibits nitric oxide production is N-nitro-L-arginine methyl ester (L-NAME), a nitric oxide synthase antagonist.

In practical terms, EGCG amplifies arginine's effect on blood flow. Even taking a large amount of pure arginine on its own doesn't boost blood flow as dramatically as you might expect — nowhere near, say, the flush you'd feel from 30 mg of niacin. The body holds a large reserve of arginine, and if most of it were suddenly converted to nitric oxide at once, that wouldn't go well — which is exactly why the body has these inhibiting mechanisms, and why they sometimes work a bit too well. Ease that inhibition slightly, though, and the effect noticeably improves. So if you want to enhance arginine's effect on blood flow, pairing it with green tea extract is a good option — whether your goal is athletic or otherwise. One catch: the green tea extract you use should be caffeine-free and should actually contain EGCG. Every manufacturer processes it differently, and most extracts do contain caffeine, while not all of them disclose their actual EGCG content.