Updated 01 July 2013

The dodgy ingredients in diet pills

Just because a slimming product contains "natural", plant-based components, it doesn't mean it's safe. DietDoc takes a look at the good, the bad and the ugly in one such product.


Just because a slimming product contains "natural", plant-based components, it doesn't mean it's safe. Health24's DietDoc, registered dietician Dr Ingrid van Heerden take a look at the good, the bad and the ugly in one such product.

One of my readers recently asked me to analyse another herbal slimming product to see if the components promote weight loss and if any of the ingredients are potentially dangerous.

Because so many people use such slimming products, I would like to share this analysis with all slimmers who are contemplating using "safe, natural, herbal slimming products".

The product in question contains the following compounds:

Evodia rutaecarpa – This is a plant extract that's used to prevent blood clotting and to stimulate the appetite. Patients on anti-clotting medications should preferably not take this plant extract as it may interfere with their medical treatment. It's not clear why an ingredient that stimulates the appetite is included in a slimming product.

Carraluma fimbriata – This is an Indian herb that has been used as "famine food" because of its appetite-suppressant properties. However, scientific studies with humans haven't as yet produced conclusive evidence that this extract will actually contribute to weight loss.

Capsicum or cayenne (chilli) – This well-known culinary ingredient is rich in vitamin C and may stimulate metabolism. However, if taken in excess, it may irritate the lining of the gastro-intestinal tract. People with stomach ulcers, gastric reflux and other acid-related stomach problems should avoid the use of large doses of chilli pepper.

Citrus aurantium (30% synephrine) – This herbal product is also known as bitter-orange extract. It's used to suppress the appetite, increase energy, lift the mood and create a "high" in users. However, like its pharmacological equivalents, epinephrine, norepinephrine and pseudoepinephrine, it can cause the following negative side-effects:

  • Nausea, vomiting and dry mouth
  • Thirst and problems with urination
  • High blood pressure
  • Rapid, irregular heartbeats (tachycardia) and even heart arrhythmias, angina pain and heart arrest
  • Restlessness, irritability, anxiety, insomnia and psychotic states
  • Dizziness, fainting and tremors
  • Flushing, muscle weakness and headaches

Contra-indications: Citrus aurantium shouldn't be used in pregnancy, during breastfeeding, or by patients with high blood pressure, hyperthyroidism, diabetes, closed-angle glaucoma, heart disease or prostate enlargement. It shouldn't be used in children and teenagers.

Special warnings:

1) Addiction:

Synephrine can be highly addictive. Because the effect wears off over time, users are inclined to take large doses to achieve the "high" and appetite-suppressant effect, thus increasing the risk of addiction.

2) Fatalities:
Reports of individuals who have died when using slimming or sports products that contain epinephrine or synephrine have lead to the banning of such products in many countries. Over-the-counter slimming and other products containing epinephrine have also been banned in South Africa and can only be obtained by medical prescription.

Be aware of the risk you run when you use synephrine. Just because it's been extracted from a plant source doesn't make it safer to use.

Fucoxanthin – This is an extract of brown seaweed, which has appetite-suppressant properties in experimental animals. This effect hasn't yet been demonstrated in humans.

Banaba – This plant extract supposedly helps to control blood-sugar levels. No scientific trials have as yet been conducted with humans.

L-tyrosine, iodo-tyrosine and diiodo-tyrosine – L-tyrosine is an amino acid that may be converted to the neurotransmitters norepinephrine and dopamine, which suppress appetite, prevent tiredness and produce a "high" in users. The amino acid L-tyrosine is classified as a non-essential amino acid because the human body is capable of producing its own L-tyrosine.

L-tyrosine is also found in large quantities in protein foods, so there's no need to take L-tyrosine supplements. Iodo- and diiodo-tyrosine are combinations of L-tyrosine and iodine, which play a role in thyroid metabolism.

Natural caffeine – Caffeine is a stimulant that has diuretic properties. When taken in excess, caffeine may cause irritability, restlessness, insomnia, anxiety and tremors. If taken without adequate liquids, the diuretic effect may be harmful. If you're sensitive to caffeine in coffee or tea, then you shouldn't take slimming pills that contain caffeine extracts. Excessive intakes can worsen stomach ulcers and irritable bowel syndrome (IBS).

Green tea extract (43% EGGG) – Scientific studies have indicated that green tea and green-tea extract, which is high in EGGG (epigallocatechin gallate) can assist weight loss. Use of EGGG is contra-indicated in patients receiving certain anticancer drugs, because it reduces their efficacy. Green tea is regarded as beneficial for certain conditions such as heart disease.

Yerba mate – This is a plant extract that's rich in xanthines such as caffeine, theophylline and theobromine, which are also found in coffee, tea and cacao. These xanthines have similar properties to caffeine (see above) and excessive intake can cause irritability and insomnia.

Bioperine – An extract of black pepper that helps with the absorption of supplements, but doesn't itself contribute to weight loss.


The above-mentioned analysis of the components of a popular herbal slimming product indicate that far from being "safe" because it's "natural", the product contains a variety of compounds that can have negative side effects.

This type of product should also not be used by women during pregnancy or during breastfeeding, by individuals with certain medical conditions, and it should certainly not be used by children and teenagers.

Always keep in mind that you can achieve weight loss without exposing your body to potentially harmful components and that some of these ingredients have already been banned in other countries.

(Dr IV van Heerden, DietDoc)

- (Health24, updated November 2012)

Any questions? Ask DietDoc


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