Weight control: Calorie-controlled diets

Jun 5th '23

Committee of Advertising Practice (CAP) understands that a calorie-controlled diet is one in which the intake of energy is lower than its output and that it is an effective way to lose weight.


  • Substantiation and efficacy claims.

Advertising rules indicate that any efficacy claims in ads for weight reduction methods, need to be supported by evidence.  Whilst it is acknowledged that calorie-controlled diets can help people lose weight, advertising claims about the effectiveness of a specific diet would need to be supported by documentary evidence.


Marketers must show that any weight-reduction is achieved by loss of body fat before making claims for weight loss. Combining a diet with an unproven weight-reduction method does not justify making weight-reduction claims for that method.


The Advertising Standards Authority (ASA) previously investigated claims that a weight-loss programme resulted in an individual achieving a 70lb weight loss were the advertiser was unable to substantiate the claims (ASC Twelve Ltd, 13 February 2019).


Marketers must hold evidence demonstrating that their diet plans are nutritionally well-balanced and the evidence should relate to the type of person who is likely to follow the diet plan. The ASA and CAP accept that normally overweight people could lose up to 2lbs a week. Except in specific circumstances, and with medical advice, weight loss should not exceed 2lbs a week when averaged over several weeks. Weight loss in the first few weeks of a calorie-controlled diet may be greater.


  • Food supplements.

Vitamins and minerals may not be offered for weight loss but may be offered to slimmer’s as a safeguard against nutritional deficiency when dieting. This is distinct from claims to use foods or foods supplements to treat clinical vitamin or mineral deficiencies, which are prohibited.


Marketers promoting Very Low Calorie Diets or other diets that fall below 800 kilo-calories a day must do so only for short-term use and must encourage users to take medical advice before embarking on them.  CAP Recommends that marketers have regard to this NICE Guidance.


Ads for weight-loss programmes which include a significant focus on foods or food supplements which are sold by the company (including meal replacement products) should not make weight loss claims about the programme unless the weight loss claims are authorised on the GB NHC Register.  See CAP Advice on Weight control: Food and food supplements.


  • Safety and social responsibility.

Claims that a rate or amount of weight loss can be achieved within a specific period of time are not permitted, irrespective of the evidence held. In 2022, the ASA upheld complaints about claims about a diet and fitness plan including: “most women easily lose 5% of their body fat in the first 14 days. You can too”, “12 weeks to rapid fat loss in Menopause” and “drop up to 40 pound of fat in just 12 weeks” (Kim Constable Ltd, 5 October 2022).


Finally, when promoting diet books, marketers should ensure their advertising is responsible. The ASA upheld a complaint about an ad that featured a book called “SIX WEEKS TO OMG, GET SKINNIER THAN ALL YOUR FRIENDS” on the grounds that it could encourage vulnerable individuals to engage in competitive dieting or unhealthy eating habits. (Michael Joseph Ltd, 3 October 2012).


  • Weight loss programmes and medicines.

Marketers should avoid combining a calorie-controlled diet with a medically-assisted programme of weight-loss which includes prescription-only medications (which cannot be advertised to the public) if the medicine is directly or indirectly referenced in the advertisement. See Weight control: Prescription-only medicines


Source: CAP


Note: This advice is given by the CAP Executive about non-broadcast advertising. It does not constitute legal advice. It does not bind CAP, CAP advisory panels or the ASA. CAP’s AdviceOnline entries provide guidance on interpreting the UK Code of Non-broadcast Advertising and Direct & Promotional Marketing.


Related: Weight control: general advertising


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