Weight loss and green tea: myth and legend

Green tea: a fat burning food for weight loss?

In the phase of weight loss, as during weight maintenance, it is important to maintain as constant as possible the daily energy expenditure.
Indeed, daily caloric consumption usually decreases during weight loss.
Since the 90s of last century, it has been proposed that green tea, thanks to  its content of caffeine and catechins, particularly epigallocatechin gallate (EGCG), which are also present in oolong tea and white tea, could be of help for:

  • maintaining , or even increasing, the daily energy expenditure;
  • increasing fat oxidation, thus acting as a fat-burning food.
Weight Loss and Green Tea
Fig. 1 – Waist Circumference

Therefore, it was attributed to green tea the ability to cause a fat loss, and so to be of help for overweight or obese adults in achieving the ideal weight.
In addition to these potential lipolytic and thermogenic effects, catechins and caffeine may be useful by acting on other targets, such as the intestinal absorption of fat and the energy intake, probably through their impact on the gut microbiota and gene expression.
Therefore, products for weight loss and weight maintenance based on green tea extracts have been marketed. It should be noted that these products contain catechins and caffeine in amount much greater than the classic drink.

How much truth is there in green tea “fat burning” properties?

The issue seems to have been resolved by a careful meta-analysis of 15 studies on weight loss and intake of these “fat burning” products.
Eight of the 15 analyzed studies were conducted in Japan, and the rest outside of Japan, for a total number of 1945 subjects, which were followed for a period of between 12 and 13 weeks.
The study showed that the consumption of green tea-based products induces, in overweight and obese adults, a weight loss that is:

  • not statistically significant;
  • very small;
  • probably not clinically important.

These “fat burning” products have not proved to be useful not even in weight maintenance.
Thus, on the basis of scientific evidence, green tea does not seem to be helpful in fat loss nor in weight maintenance.
There are no magic bullets: the only way to lose weight (body fat) and avoid future increases is to control your daily calorie intake and take part in physical activity on a regular basis.

References

Hursel R. and Westerterp-Plantenga M.S. Catechin- and caffeine-rich teas for control of body weight in humans. Am J Clin Nutr 2013;98:1682S-1693S doi:10.3945/ajcn.113.058396

Hursel R., Viechtbauer W. and Westerterp-Plantenga M.S. The effects of green tea on weight loss and weight maintenance: a meta-analysis. Int J Obesity 2009;33:956-961 doi:10.1038/ijo.2009.135

Jurgens T.M., Whelan A.M., Killian L., Doucette S., Kirk S., Foy E. Green tea for weight loss and weight maintenance in overweight or obese adults. Editorial group: Cochrane Metabolic and Endocrine Disorders Group. 2012:12 Art. No.: CD008650 doi:10.1002/14651858.CD008650.pub2

Skin, blood pressure, rheumatoid arthritis and gamma-linolenic acid

Healthy skin and gamma-linolenic acid

gamma-Linolenic acid (GLA), an omega-6 essential fatty acid, like its precursor linoleic acid (the most abundant polyunsaturated fatty acid in human skin epidermis, where it’s involved in the maintenance of the epidermal water barrier), plays important roles in the physiology and pathophysiology of the skin.
Studies conducted on humans revealed that gamma-linolenic acid:

  • improves skin moisture, firmness, roughness;
  • decreases transepidermal water loss (one of the abnormalities of the skin in essential fatty acid deficiency animals).
Skin and gamma-Linolenic Acid
GLA

Using guinea pig skin epidermis as a model of human epidermis (they are functionally similar), it was demonstrated that supplementation of animals with gamma-linolenic acid-rich foods results in a major production of PGE1 and 15-HETrE in the skin (as previously demonstrated in in vitro experiments).
Because these molecules have both anti-inflammatory/anti-proliferative properties supplementation of diet with gamma-linolenic acid acid-rich foods may be an adjuncts to standard therapy for inflammatory/proliferative skin disorders.

Supplemental sources of GLA

The main supplemental sources of gamma-linolenic acid are oils of the seeds of:

  • borage (20%-27% of the total fatty acids);
  • black currant (from 15% to 19% of the total fatty acids);
  • evening primrose (from 7% to 14% of the total fatty acids), and

Role of gamma-linolenic acid in lowering blood pressure

The relationship between dietary fatty acid intake and blood pressure mainly comes from studies conducted on genetically modified rats that spontaneously develops hypertension (a commonly used animal model for human hypertension).
In these studies many membrane abnormalities were seen so hypertension in rat model may be related to change in polyunsaturated fatty acid metabolism at cell membrane level.
About polyunsaturated fatty acids, several research teams have reported that gamma-linolenic acid reduces blood pressure in normal and genetically modified rats (greater effect) and it was purported by interfering with Renin-Angiotensin System (that promote vascular resistance and renal retention) altering the properties of the vascular smooth muscle cell membrane and so interfering with the action of angiotensin II.
Another possible mechanism of action of gamma-linolenic acid to lower blood pressure could be by its metabolite dihomo-gamma-linolenic acid: it may be incorporated in vascular smooth muscle cell membrane phospholipids, then released by the action of phospholipase A2 and transformed by COX-1 in PGE1 that induces vascular smooth muscle relaxation.

Role gamma-linolenic acid in treatment of rheumatoid arthritis

In a study conducted by Leventhal et al. on 1993 it was demonstrated the dietary intake of higher concentration of borage oil (about 1400 mg of gamma-linolenic acid/day) for 24 weeks resulted in clinically significant reductions in signs and symptoms of rheumatoid arthritis activity.
In a subsequent study by Zurier et al. on 1996 the dietary intake of an higher dose (about 2.8 g/day gamma-linolenic acid) for 6 months reduced, in a clinically relevant manner, signs and symptoms of the disease activity; patients who remained for 1 year on the 2.8 g/day dietary gamma-linolenic acid exhibited continued improvement in symptoms (the use of gamma-linolenic acid also at the above higher dose is well tolerated, with minimal deleterious effects). These data underscore that the daily amount and the duration of gamma-linolenic acid dietary intake do correlate with the clinical efficacy.

References

Akoh C.C. and Min D.B. “Food lipids: chemistry, nutrition, and biotechnology” 3th ed. 2008

Chow Ching K. “Fatty acids in foods and their health implication” 3th ed. 2008

Fan Y.Y. and Chapkin R.S. Importance of dietary γ-linolenic acid in human health and nutrition. J Nutr 1998;128:1411-14. doi:10.1093/jn/128.9.1411

Leventhal L.J., Boyce E.G. and Zurier R.B. Treatment of rheumatoid arthritis with gammalinolenic acid. Ann Intern Med 1993 119:867-73. doi:10.7326/0003-4819-119-9-199311010-00001

Miller C.C. and Ziboh V.A. Gammalinolenic acid-enriched diet alters cutaneous eicosanoids. Biochem Biophys Res Commun 1988 154:967-74. doi:10.1016/0006-291X(88)90234-3

Zurier R.B., Rossetti R.G., Jacobson E.W., DeMarco D.M., Liu N.Y., Temming J.E., White B.M. and Laposata M. Gamma-linolenic acid treatment of rheumatoid arthritis. A randomized, placebocontrolled trial. Arthritis Rheum 1996 39:1808-17. doi:10.1002/art.1780391106