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The Truth About Fad Diets and Dietary Supplements for Weight Loss

Category: Healthy eating, healthy weight and dieting
Healthy eating, healthy weight and dieting

The idea of "fast and easy" weight loss sounds good to everyone. If only it were that simple! There are many fad diets and diet supplements that claim rapid and prolonged weight loss. When looking at the evidence, we need to find out if these diets or supplements are medically safe. Always ask a doctor or registered dietitian for their opinion if you have concerns.




A recent medical journal reviewed several diet supplements that are currently used for weight loss. The results are worrying. It was found that some ingredients used in these supplements could be harmful for example ephedra or ephedrine can double or treble the risk of developing psychiatric symptoms, stomach problems and heart palpitations. In general the evidence for many weight loss diet supplements is not strong therefore their use is not recommended without medical supervision.




The INDI and HSE recommend that eating foods from all food groups are essential for good health and weight management. Many fad diets that remove certain food groups or nutrients are therefore considered by health professionals to be unhealthy.


Be Aware of…

  • Very Low Calorie Diets (VLCDs); these are diets that contain less than 800 kcals per day. This pattern of restrictive eating should only be carried out under medical supervision; this is because it can result in heart rhythm abnormalities, which can be fatal. Common side effects include: fatigue, weakness, dizziness, constipation, hair loss, dry skin, brittle nails, nausea, diarrhoea, changes in periods, oedema, and cold intolerance. For more information, see factsheet on VLCD’s.
  • Short term fad diets (see below); diets like these that offer long term weight loss are most likely untrue. In order to truly keep weight off in the long term, continuous changes to your lifestyle and activity patterns must be made. These cannot be replaced with a “quick fix”.
  • Miracle foods; diets that recommend certain foods for their “special” "breakthrough", “fat-burning”, "metabolic" or "secret ingredient” are most likely untrue. It is not possible to increase your metabolism or burn fat using one single food. If it sounds too good to be true, it probably is!


Examples of Fad Diets

Type Examples Evidence
Low carbohydrate Diet/ low carb diets Atkins, Zone, Scardale Over   a 12 month period, evidence shows little different between low carbohydrate   diet and general low calorie diet. In fact, low calorie diets has been show   to have a greater reduction in LDL cholesterol than a low carbohydrate diet.   Low carbohydrate diets have many side effects and should be carried out under   strict medical supervision.
Low GI Diets The GI diet Following   a Low GI diet for weight loss without energy restriction has poor results.   However a low GI diet can help control blood glucose and insulin function   better than an average diet.
Detox Diets/Juice diets 21 day cleanse, Juice diet Cleansing   plans tend to be dangerously low in calories <900kcals. This means you   will not meet your full requirements for many essential nutrients. Side   effects include fatigue, GI upset, dizziness, and nausea.
High Protein Diets Paleo diet A   high protein diet is defined as >20% of daily energy intake coming from   protein sources. Without an overall energy restriction high protein diets   will not lead to weight loss.
Fasting Diets 5:2 diet For   everyday active person, fasting diets may present challenges such as feeling   light headed, tired and dizzy. Consuming too few calories will make it hard   to exercise for prolonged periods.



Created by members of the weight management interest group, May 2016

Review date: May 2019.

© 2016 Irish Nutrition and Dietetics Institute, INDI. All rights reserved. May be reproduced in its entirety provided the source is acknowledged. This information is not meant to replace advice from your medical doctor or individual counseling with a dietitian. It is intended for educational and informational purposes only.

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