It’s official: Christmas is terrible for the waistline.
The US Human Nutrition Research Center found that, among the entire population, weight gain during the six-week holiday season (from Thanksgiving to New Year) accounted for 51 per cent of the annual weight gain. In addition, 14 per cent gained more than five pounds, with such weight gain being greater among those who were already overweight or obese (Nutr Rev, 2000; 58: 378-9).
In the attempt to shed excess pounds, many people look for a quick fix in the form of natural slimming aids, which typically promise to help you burn fat, increase your metabolism and control your appetite – sometimes all in one pill.
But do these products work? Here’s a handy guide to some common ingredients used in such supplements.
In a double-blind, controlled Japanese study, catechins, the active ingredients in green-tea extract, reduced body fat when taken every day. The 38 healthy male participants (aged 24-46) were divided according to body mass index (BMI) and waist size. One group consumed oolong tea with 690 mg of catechins from green-tea extract; the other drank the oolong tea with only 22 mg of green-tea catechins. After 12 weeks, BMI, weight, waist size, and body and subcutaneous fat were all significantly lower in those taking the higher dose of catechins (Am J Clin Nutr, 2005; 81: 122-9).
Another study found that green-tea extract rich in catechins – taken at breakfast, lunch and dinner – increased the number of fat calories burned per day. The scientists concluded that green tea has thermogenic properties – in other words, it’s a metabolism booster. More important, green-tea extract doesn’t cause an increase in heart rate, a side-effect typically seen with stimulant-based slimming products (Am J Clin Nutr, 1999; 70: 1040-5).
The side-effects of excess green-tea consumption (more than 8 cups/ day) are minor, including gas, an upset stomach, nausea, heartburn, abdominal pain, dizziness, headache and muscle pain.
Hydroxycitric acid (HCA), found in the Malabar tamarind fruit (Garcinia cambogia), is a popular ingredient in natural slimming aids. In places where it’s regularly used in cooking, such as Southeast Asia, it is said to make food apparently more ‘filling’ (Gene Expr, 2004; 11: 251-62).
Placebo-controlled studies have found that HCA can indeed increase weight loss and reduce appetite (Int J Obes, 1997; 21 [Suppl 2]: S61; Diabetes Obes Metab, 2004; 6: 171-80), lower calorie intake (Int J Obes Relat Metab Disord, 2002; 26: 870-2) and increase fat-burning in athletes (J Nutr Sci Vitaminol [Tokyo], 2002; 48: 128-33). One study reported increased weight loss after treatment with HCA plus chromium (Am J Bariatr Med, 1993; Summer: 17-9).
However, recent reports suggest that HCA effectiveness may depend on the dosage and type of HCA formulations used. For example, in rat studies (and so not necessarily applicable to humans), Dutch scientists have found that the HCA-based products Citrin K and Regulator were significantly more effective than Super CitriMax HCA-600-SXS at reducing food intake, despite the use of the same dosages of 150 and 300 mg/kg (Nutr Metab [Lond], 2005; 2: 23). It’s worth investigating the evidence of success before you buy.
7-Keto-DHEA has been found to yield significant weight loss when combined with one hour of cross-training exercise three times a week. Compared with an exercise-placebo group, the participants taking the DHEA lost three times more weight over an eight-week period (J Exerc Physiol [online], 1999; 2: ISSN 1097-9751). Other studies – albeit in rats – report better thyroid function and greater thermogenesis (heat generation that can include burning excess food calories) following 7-oxo-DHEA administration (Proc Natl Acad Sci USA, 1995; 92: 6617-9; Arch Biochem Biophys, 1997; 341: 122-8).
Proceed with caution
Conjugated linoleic acid (CLA)
This naturally occurring fatty acid is found in animals, plants and, now, slimming supplements because of its potential for increasing lean tissue mass while reducing fat storage. Its effectiveness is supported by numerous animal studies (Am J Physiol, 1999; 276: R1172-9; Br J Nutr, 2003; 89: 219-29), and the human data are promising. For example, a one-year, double-blind, placebo-controlled study of 180 overweight men and women found that long-term supplementation with CLA (either as part of a triglyceride or as the free fatty acid) reduced body fat, and was well tolerated – even without dieting or exercise (Am J Clin Nutr, 2004; 79: 1118-25).
However, there are concerns that the use of CLA by overweight people could increase insulin resistance and, thus, the risk of developing diabetes.
The evidence is mixed as to whether or not chromium is an effective aid for weight loss or improving the body’s fat-to-lean-tissue ratio. In one study, 154 people were given either a placebo, or 200 or 400 mcg/day of chromium picolinate. After 72 days, those taking chromium achieved significantly greater weight loss than those taking the placebo (more than 2.5 lb vs about 0.25 lb). They also gained lean body mass (Curr Ther Res Clin Exp [USA], 1996; 57/10: 747-65).
However, other, smaller studies have failed to find the same effects (Med Sci Sports Exerc, 1996; 28: 139-44). Furthermore, the long-term effects of chromium accumulation in the body are uncertain.
Many studies have found that the Chinese herb ma huang (Ephedra sinica) prompts the body to burn up energy (calories) faster, leading to weight loss (Int J Obes, 1987; 11: 163-8).
However, an investigation commissioned by the US Food and Drug Administration found that natural diet supplements containing the herb can cause cardiovascular problems such as hypertension and palpitations. Death and disability made up more than a quarter (26 per cent) of all reported adverse effects that were definitely, probably or possibly associated with Ephedra (N Engl J Med, 2000; 343: 1833-8).