Clare Collins, University of Newcastle; Lee Ashton, University of Newcastle, and Rebecca Williams, University of Newcastle
When you google “weight loss” the challenge to sort fact from fiction begins. These five supplements claim to speed up weight loss, but let’s see what the evidence says.
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1. Raspberry ketones
Raspberry ketones, sold as weight loss tablets, are chemicals found in red raspberries responsible for that distinct raspberry flavour and smell. You can also make raspberry ketones in a lab.
Only 45 participants completed the study. The 27 who took a supplement lost about 1.9 kilos, compared to 400 grams in the 18 in the placebo group. The drop-out rate was so high that these results need to be interpreted with a lot of caution.
A
small pilot study of five adults found no effect on weight when the participants were told to maintain their current eating and exercise patterns and just took supplements of 200mg/day of raspberry ketones.
Matcha is a green tea made from leaves of the Camellia sinensis, or tea plant, but it’s processed into a green powder and can be mixed into liquids or food. Before the leaves are harvested, the tea plant is put in the shade for a few weeks, which increases the content of theanine and caffeine.
No studies have tested the effect of matcha on weight loss. A
review of six studies using green tea preparations for weight loss over 12 weeks found a difference based on country. In studies conducted outside of Japan, people consuming green tea did not lose more weight than controls. In the eight studies conducted within Japan, the mean weight loss ranged from 200 grams to 3.5 kilos in favour of green tea preparations.
3. Garcinia cambogia supplements
In
animal studies, HCA interferes with usual production of fatty acids. If this was transferred to humans it could theoretically make it harder to metabolise fat and speed up weight loss. Research studies in humans show this is not the case.
While one
12-week trial in overweight women randomised them to a low kilojoule diet, with or without HCA and found the HCA group lost significantly more weight (3.7 compared to 2.4 kilos for placebo), two other trials found no difference in weight loss.
The lowest caffeine dose of 100mg, the amount in one instant coffee, increased the average metabolic rate by nine calories per hour, while the 400mg dose, which is roughly equivalent to the caffeine found in two to three cups of barista-made coffee, increased metabolic rate by about 34 calories per hour over three hours.
Alkalising products are promoted widely. These include alkaline water, alkalising powders and
alkaline diets. You’re supposed to measure the acidity of your urine and/or saliva to “assess” body acidity level. Urine usually has a slightly acidic pH (average is about pH6) – vegetables and fruit make it more alkaline, while eating meat makes it less so.
Saliva has a neutral pH of 7. Alkaline diets recommend you modify what you eat based on your urine or saliva pH, claiming a more alkaline pH helps digestion, weight loss and well-being.
If you’d like to learn more about weight loss enrol in our free six week online course The Science of Weight Loss – Dispelling Diet Myths, here.
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