No doubt plenty of us have been tempted by a slimming supplement at some point in our lives. Indeed, an American survey published in 2008 found that more than a third of adults who made a weight-loss attempt had used a dietary supplement to do so (J Obes, 2011; pii: 297315).
With many products claiming to tone you up and trim you down with minimal effort and no risk, it’s little wonder they’re so popular. But do any of them actually work? And are they really safe?
Here are some of the most popular natural slimming supplements and the science-or lack of it-behind them.
CLA
- The pill: Conjugated linoleic acid (CLA) is a fatty acid found in the meat and milk of grazing animals. The US Food and Drug Administration (FDA) recently approved CLA for its ‘generally recognized as safe’ category, which means that it can now be used in various foods and drinks. It’s also found in numerous supplements aimed at slimmers and bodybuilders.
- The promise: CLA is said to reduce body fat storage and to increase lean muscle mass while boosting fat breakdown.
- The proof: Studies in mice show that those given CLA lose significant amounts of body fat and show an increase in lean body mass (Am J Clin Nutr, 2007; 85: 1203-11; Lipids, 1997; 32: 853-8). However, results in human trials have been mixed. In one, 60 overweight or obese men and women were given either 9 g of olive oil (placebo) or one of four doses of CLA (1.7 g/day, 3.4 g/day, 5.1 g/day or 6.8 g/day) for 12 weeks. Compared with the controls, all of those taking CLA-regardless of dose-reduced body fat, although the results were most significant in those taking 3.4 g/day or more (J Nutr, 2000; 130: 2943-8). In another trial, taking CLA (5 g/day) during resistance training resulted in small, but statistically significant, increases in lean body mass and greater losses of fat mass after seven weeks compared with a placebo (Med Sci Sports Exerc, 2006; 38: 339-48). Other studies, however, have failed to find any significant benefit with CLA (Lipids, 2000; 35: 777-82; J Strength Cond Res, 2002; 16: 325-34). Fortunately, US researchers have attempted to make sense of the conflicting research by conducting a pooled analysis of all high-quality clinical trials (they were randomized, double-blind and placebo-controlled) on CLA. They concluded that CLA has a ‘modest’ effect on human body composition, with a dose of around 3 g/day resulting in a fat loss of around 0.09 kg/week (Am J Clin Nutr, 2007; 85: 1203-11). So, it’s hardly a quick-fix solution. Also, CLA doesn’t appear to have much effect on either body weight or body mass index (BMI) (J Obes, 2011; pii: 297315).
- Precautions: CLA appears to be safe, with the most common side-effects being gastrointestinal. However, there are some concerns that the use of such supplements by overweight people could cause or aggravate insulin resistance, which might then increase the risk of developing diabetes (Am J Clin Nutr, 2007; 85: 1203-11; Circulation, 2002; 106: 1925-9). Other research suggests that CLA might lower levels of ‘good’ (HDL) cholesterol while contributing to inflammation and oxidative stress (Crit Rev Food Sci Nutr, 2006; 46: 479-88).
No doubt plenty of us have been tempted by a slimming supplement at some point in our lives. Indeed, an American survey published in 2008 found that more than a third of adults who made a weight-loss attempt had used a dietary supplement to do so
(J Obes, 2011; pii: 297315).
With many products claiming to tone you up and trim you down with minimal effort and no risk, it’s little wonder they’re so popular. But do any of them actually work? And are they really safe?
Here are some of the most popular natural slimming supplements and the science-or lack of it-behind them.
CLA
u The pill: Conjugated linoleic acid (CLA) is a fatty acid found in the meat and milk of grazing animals. The US Food and Drug Administration (FDA) recently approved CLA for its ‘generally recognized as safe’ category, which means that it can now be used in various foods and drinks. It’s also found in numerous supplements aimed at slimmers and bodybuilders.
u The promise: CLA is said to reduce body fat storage and to increase lean muscle mass while boosting fat breakdown.
u The proof: Studies in mice show that those given CLA lose significant amounts of body fat and show an increase in lean body mass (Am J Clin Nutr, 2007; 85: 1203-11; Lipids, 1997; 32: 853-8). However, results in human trials have been mixed.
In one, 60 overweight or obese men and women were given either 9 g of olive oil (placebo) or one of four doses of CLA (1.7 g/day, 3.4 g/day, 5.1 g/day or 6.8 g/day) for 12 weeks. Compared with the controls, all of those taking CLA-regardless of dose-reduced body fat, although the results were most significant in those taking 3.4 g/day or more (J Nutr, 2000; 130: 2943-8). In another trial, taking CLA (5 g/day) during resistance training resulted in small, but statistically significant, increases in lean body mass and greater losses of fat mass after seven weeks compared with a placebo (Med Sci Sports Exerc, 2006; 38: 339-48).
Other studies, however, have failed to find any significant benefit with CLA (Lipids, 2000; 35: 777-82; J Strength Cond Res, 2002; 16: 325-34).
Fortunately, US researchers have attempted to make sense of the conflicting research by conducting a pooled analysis of all high-quality clinical trials (they
were randomized, double-blind and placebo-controlled) on CLA. They concluded that CLA has a ‘modest’ effect on human body composition, with a dose of around 3 g/day resulting in a fat loss of around 0.09 kg/week (Am J Clin Nutr, 2007; 85: 1203-11). So, it’s hardly a quick-fix solution. Also, CLA doesn’t appear to have much effect on either body weight or body mass index (BMI) (J Obes, 2011; pii: 297315).
u Precautions: CLA appears to be safe, with the most common side-effects being gastrointestinal. However, there are some concerns that the use of such supplements by overweight people could cause or aggravate insulin resistance, which might then increase the risk of developing diabetes (Am J Clin Nutr, 2007; 85: 1203-11; Circulation, 2002; 106: 1925-9). Other research suggests that CLA might lower levels of ‘good’ (HDL) cholesterol while contributing to inflammation and oxidative stress (Crit Rev Food Sci Nutr, 2006; 46: 479-88).
Green-tea extract
- The pill: Green-tea extract (GTE) contains catechins, active compounds present in the unfermented dried leaves of Camellia sinensis. It’s credited with a range of bene-fits, including weight loss, and is the fourth most popular dietary supplement in the US.
- The promise: GTE supposedly increases calorie and fat metabolism while decreasing appetite. It’s thought to act mainly on the sympathetic nervous system, which deter-mines calorie expenditure.
- The proof: In a double-blind, controlled Japanese study, 35 healthy men were divided by BMI and waist size. One group drank oolong tea with 690 mg of catechins from GTE; the other drank oolong tea with only 22 mg of GTE catechins. After 12 weeks, BMI, weight, waist size and body 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 a GTE 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. They also noted that it caused no increase in heart rate, a side-effect typically seen with stimulant-based slimming products (Am J Clin Nutr, 1999; 70: 1040-5). More recently, a meta-analysis concluded that GTE catechins are effective for reducing BMI, body weight and waist size, but the effects are modest at best. Moreover, it revealed that the catechins only work if the caffeine has not been removed, suggesting that this may be contribu-ting to the weight loss (Am J Clin Nutr, 2010; 91: 73-81).
Precautions: Excess green-tea consumption (more than eight cups a day) can cause minor side-effects, including upset stomach, nausea and heartburn. But more worrying is the link between green-tea prod-ucts and liver damage. However, a review by the US Pharmacopeia stated that GTE products appear to be safe as long as they are used and formulated appropriately (Drug Saf, 2008; 31: 469-84). If you wish to try GTE, make sure you go for a reputable brand and take it as directed. Also, avoid taking the supplement on an empty stomach.
Hoodia
- The pill: Hoodia gordonii was once a little-known plant native to the Kalahari desert in South Africa. Now, the herb is found in slimming products worldwide, ranging from capsules and tablets to tinctures and syrups.
- The promise: Hoodia is claimed to encourage weight loss by suppressing the appetite. According to one website promoting the supplement, with Hoodia, you “can make cravings vanish, reduce your calorie intake substantially, and lose body fat”.
- The proof: Despite being one of the most widely used slimming supplements today, there’s actually little scientific evidence to show that the herb helps weight loss.
Researchers began studying Hoodia in the early 1960s and, some 20 years later, isolated an extract they dubbed ‘P57’, which was believed to stimulate feelings of satiety in the brain. Yet, so far, there are still no published clinical trials of the extract.
Websites selling Hoodia often cite a trial showing that, after two weeks, volunteers taking the herb ate 1000 fewer calories a day than those taking a placebo. However, the study involved only 18 people, was never peer-reviewed or published, and was sponsored by Phytopharm, a British biopharmaceutical company licensed to develop P57 on a large scale (Harv Womens Health Watch, 2008; 15: 8). The results, therefore, need to be viewed with caution.
On the upside, there’s published evidence in animals that Hoodia may work.
South African researchers tested the plant extract against appetite-suppressing fenfluramine (now banned due to heart risks) in rats-so the findings may not necessarily apply to humans-and found that Hoodia reduced food intake and also led to weight loss. Fenfluramine, on the other hand, reduced food intake only slightly and led to weight gain (Phytochemistry, 2007; 68: 2545-53).
In another rat study, US scientists injected P57 directly into the brain. Food intake was reduced by 40-60 per cent over 24 hours, and levels of ATP (adenosine triphosphate) in the hypothalamus-which controls hunger-were increased. This ATP upregulation may lie behind the herb’s apparent appetite-suppressing effects (Brain Res, 2004; 1020: 1-11).
Nevertheless, although this is all highly promising, until more reliable human trials are published, we won’t know whether Hoodia-and, specifically, Hoodia in pill form-will work in overweight people as it does in rats.
- Precautions: As clinical trials are lacking, we’re completely in the dark about the herb’s safety. Another concern is that the products currently available aren’t regulated, so it’s unclear how much of the herb-if any-they contain. Experts argue that there simply aren’t enough Hoodia plants in the world to account for all the alleged Hoodia products now on the market. And not only may they contain little or no H. gordonii, they may also include the wrong parts of the plant or use questionable plant sources (Harv Womens Health Watch, 2008; 15: 8). In fact, independent laboratory tests by Alkemists Pharmaceuticals in California have revealed that around two-thirds of the supplements on the US marketplace contained no identifiable H. gordonii whatsoever (www.naturalnews.com/011425.html).
Joanna Evans
WDDTY VOL. 22 NO. 5
