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Americans are heavily investing in their weight loss goals, spending an average of $2 billion annually on weight loss supplements. It is no surprise however, given that the marketing claims for these little pills sometimes seem too good to be true. Unfortunately, there is not much evidence to support that these supplements can help with long-term weight loss. Typically, they rely on four mechanisms: (1) block carbohydrate or fat absorption, (2) increase metabolism, (3) change body composition, or (4) suppress appetite. Let’s dive a little further into the research on five of the most common weight loss supplements to evaluate their claims.

Carnitine

Carnitine is a substance in the body that is mostly found in skeletal and heart muscle. When it comes to fat metabolism, carnitine is responsible for shuttling fat, specifically long-chain fatty acids, into the mitochondria so they can be broken down into a byproduct used as energy for most tissues. Thus came the assumptions that increasing carnitine levels could potentially increase fat metabolism. While many studies have shown that oral carnitine ingestion does not change muscle carnitine levels, one study did demonstrate that carnitine levels increased through oral ingestion of carnitine only when combined with large amounts of carbohydrates. The results from the latter study did reveal small improvements of fat metabolism in the long term. However, it seems a bit counterproductive to use this technique for weight loss, unless possibly for athletes, since it requires consuming large amounts of carbohydrates. Overall, there is still not enough evidence to support the claims that carnitine supplementation can improve fat metabolism and assist with weight loss in humans. Furthermore, L-carnitine is a metabolic precursor to trimethylamine-N-oxide (TMAO), a metabolite that can be produced by intestinal microbiota when digesting L-carnitine. Dietary L-carnitine supplementation can significantly increase TMAO levels in humans and rodents, and some studies have suggested that L-carnitine may be a link between red meat consumption and atherosclerosis development. In addition, TMAO has been associated with an increased risk of a number of diseases, including cardiovascular disease, heart attack, stroke, and chronic kidney disease.

CLA

Conjugated linoleic acid (CLA) is a naturally occurring omega-6 fatty acid found in the milk and meat of some animals. It is suggested that CLA can decrease fat production, increase energy expenditure and fat metabolism. Studies in rodents have supported these claims, revealing that CLA supplementation can reduce body fat by 44% after ingesting it for just four weeks. However, for these effects to be apparent in humans, individuals would have to supplement much larger doses of CLA for a much longer period of time. In one study with overweight men and women, researchers found that consuming high doses (3 g) of CLA significantly reduced body fat mass after 6 and 12 months compared to placebo. However, a meta-analysis on 18 studies evaluating CLA supplementation of varying dosages could not come up with conclusive evidence to support any influence on body composition. Generally, it appears that supplementing with around 3 g of CLA daily may lead to modest fat loss based on clinical trials, but future studies should address the safety issues regarding chronic supplementation.

Green Tea

Green tea contains compounds known as a catechins that are thought to stimulate fat oxidation. Short-term studies on green tea extract ingestion have revealed that the catechins in green tea, specifically EGCG, may have the potential to increase fat oxidation at rest in as short as over a 24-hour period, independent of its caffeine content. Other studies demonstrate that when paired with caffeine, the effects of fat oxidation appear to be enhanced by up to 16%. Interestingly, longer term studies reveal that ingesting green tea extract for 13 weeks led to an average weight loss of 1.3 kg. This effect was heightened in a group that consumed low caffeine compared to another group consuming moderate levels of caffeine. Thus, it does seem that GTE has the potential to increase fat oxidation at rest, but the evidence still remains inconclusive regarding the effective dosage, duration and whether or not the simultaneous consumption of caffeine has a promising effect.

Chromium

Chromium is an essential trace element that has received a lot of attention lately for its purported ability to ‘build muscle’ and ‘burn fat.’ Only one human study can confirm this claim. Evans and researchers were the first to identify alterations in body composition after their subjects supplemented with chromium picolinate for a little over a month. The experimental group, which consisted of college students and athletes, revealed a significant increase in lean body mass compared to the placebo group. However, further investigations have not been able to support these findings. For example, another study revealed that chromium supplementation did not independently influence changes in body weight or composition when paired with a low-energy diet. Thus, the majority of studies cannot conclusively support the claims made about chromium supplementation for weight loss.

Probiotics

There is considerable scientific evidence to suggest that the tiny microorganisms that reside in the gut may play a role in body weight regulation. People with obesity not only appear to have less diverse gut bacteria than lean people, but they also tend to gain more weight as well. Probiotic supplementation has varying effects on body weight, depending on the strain. One strain in particular, Lactobacillus gasseri, has been shown to have some of the most promising effects. One study demonstrated that individuals taking this strain reduced body weight and BMI after 12 weeks. It has been suggested that these effects may be related to the strain’s influence on appetite-regulating hormones (such as GLP-1) and fat-regulating proteins. In general, probiotics may also reduce the number of calories absorbed from food and potentially reduce inflammation. Overall, certain types of probiotics may have a modest influence on weight loss, especially when combined with a healthy diet and regular exercise.

In summary, despite their popularity amongst consumers and the profitability for their manufacturers, weight loss supplements cannot be considered an important part of an effective and sustained weight loss strategy. Greater awareness of the role of harmful dietary components that underlie the current obesity epidemic, such as the role of ultra processed foods, sugars, non-nutritive sweeteners, and portion sizes, and switching to a healthy largely plant-based diet, combined with regular daily exercise remains the most prudent way to return to and maintain a normal body weight.