In this second post I want to look in detail at the responses that Zoe Harcombe provided to the Advertising Standards Authority (ASA) to support the claim that the Harcombe Diet  leads to weight loss*.
But before I do that, I want to identify some fundamental principles of an evidence based approach which we might use to appraise claims.
- The burden of proof rests squarely on the person making a claim. This is a basic principle of scientific and reasoned argument and not co-incidentally, is how the ASA investigation process works (They expect an advertiser to hold robust evidence before making a claim).
- Evidence to support any claim should be of a high quality. There are many aspects to this, but in its simplest form this means avoiding making claims based upon evidence which we know is likely to be subject to significant bias or errors.
Via the ASA complaint process I challenged  whether:
…the implication in the testimonials in ad (d) that the Harcombe diet led to weight loss could be substantiated
Here is advertisement (d) and the testimonials in question, as they looked in July 2014:
In response to this Zoe Harcombe :
…said the testimonials were direct quotations from the book ‘Stop Counting Calories & Start Losing Weight’ and that they would amend the ad to make clear they were book extracts
Now there are two possibilities here: i) Zoe entirely missed the point that it is the use of testimonials to make objective adversing claims which is the problem rather than their source, or ii) she tried an unedifying manoeuvre in a bid to re-frame her advertising claims so as to put them outside the remit of the advertising regulator.
Lets look at both possibilities.
On the use of testimonials, I will spell it out: anecdotal evidence is one of the very weakest forms of evidence available to us, because by its nature it is uncontrolled and subject to a number of biases which mean it is not representative of the ‘typical’ experience. It is for these reasons that testimonials should not be used to support a generalised claim about the efficacy of a weight loss method.
Just to show I am not misrepresenting Zoes position, here is her response to the ASA from the previous investigation in June 2014 :
ZH said that the diet did work, and that they regularly receive feedback telling them that. They provided copies of some unsolicited feedback they had received…[…]…They said that the person who informed them of the “17lb in 5 days ” weight loss had done so so unsolicited.
Aside from the bald assertion, it doesn’t appears to have dawned on Zoe that unsolicited letters from dieters are not only entirely uncontrolled accounts (we have no idea what other variables changed which may have contributed to that success), but are also a self selected sample which will probably more strongly favour those who were successful and thus felt motivated to share their experiences with her.
What about those who don’t write letters? Do dieters ever write to authors telling them it didn’t work? If so why does the marketing for the Harcombe Diet not include a representative proportion of these? This really is basic stuff and is exactly why the CAP Codes expressly point out that testimonials should not be used for to support objective claims.
If alternatively Zoes response was simply attempting to take the claims outside the ASA’s remit, then I have to conclude that would represent a cynical attempt to avoid the burden of proof. If the claims in her book are based on robust evidence and meet the standards of good science, then they should also stand up to the comparable (more on that later) scrutiny of an ASA investigation.
We should demand so much more of self appointed diet ‘experts’. Do we want to take advice from those who evade reasonable requests for evidence while applying that standard to others, or do we want those who recognise the burden of proof and invite scrutiny of the evidential basis of their own claims?
In the light of the above, it is unsurprising that the ASA adjudicated that :
Ad (d) included testimonials which referred to weight loss and we therefore considered that consumers would understand that undertaking the Harcombe diet would lead to weight loss. The CAP Code stated that any claim made for the effectiveness of a weight-reduction method must be backed, if applicable, by rigorous trials on people, and that testimonials were not sufficient to support such claims. We noted Zoë Harcombe said they would amend the claims to make clear they were book extracts, but were concerned that any such quotes were still likely to imply efficacy. We had not been provided with any evidence that the Harcombe diet, which we understood did not rely on calorie reduction, led to weight loss and therefore concluded that the testimonials breached the Code.
On this point ad (d) breached CAP Code (Edition 12) rules 3.1 (Misleading advertising), 3.7 (Substantiation) and 13.1 (Weight control and slimming).
Now in her defence Zoe has gone to great lengths to attempt to discredit the CAP Codes . While I don’t think that the CAP Advertising Codes are perfect, I believe that in general they have some sensible principles which are important for consumer protection. It is therefore worth looking in detail at the breaches identified to see if she has a case.
Here are the first two Code requirements  which were breached:
3.1 Marketing communications must not materially mislead or be likely to do so.
Could anyone reasonably argue that marketing communications should not mislead?
3.7 Before distributing or submitting a marketing communication for publication, marketers must hold documentary evidence to prove claims that consumers are likely to regard as objective and that are capable of objective substantiation. The ASA may regard claims as misleading in the absence of adequate substantiation.
Are the claims in advertisement (d) not likely to be taken as an objective claims by consumers? You may disagree but I suspect how much will I lose? is probably the first and most important question people ask before embarking on any weight loss diet. The requirement for adequate substantiation (as noted below) in my opinion is simply a reasonable application of the burden of proof to an advertising claim and I fail to see how such fundamental principles can be wrong.
What about the more specific CAP rules on weight loss  which Zoe asserts  are invalid?:
13.1 A weight-reduction regime in which the intake of energy is lower than its output is the most common self-treatment for achieving weight reduction. Any claim made for the effectiveness or action of a weight-reduction method or product must be backed, if applicable, by rigorous trials on people; testimonials that are not supported by trials do not constitute substantiation
The first thing to note here is that compliance with this requirement is not contingent in any way on accepting what Zoe terms the ‘calorie theory’ (that a 3,500 kcal deficit in energy will lead to a 1 lb weight loss**), it simply infers that a calorie deficit is the most common approach which is likely to be used to achieve weight loss, but states that where applicable claims of efficacy for any method must be backed by human trial data.
Far from being against ‘non-conventional’ advice, what we have here is an entirely level playing field where any weight loss method which can be substantiated is not misleading. I suppose you could argue that a small diet business does not have the resources to conduct a suitably powered Randomised Controlled Trial (RCT) which might be capable of satisfying the ASA, but that I am afraid, appears to be the cost of making objective claims about weight loss. This certainly isn’t an argument for providing only the flimsiest of supporting evidence.
So in summary we have seen that:-
- The claims that the Harcombe Diet leads to weight loss are by Zoes own admission based only on self selected anecdotal evidence, which may be biased and cannot be use to support generalised claims of efficacy.
- Zoe Harcombe appears to have attempted to re-frame her claims to avoid scrutiny.
- The CAP Codes require substantiation in line with a reasonable burden of proof
- The CAP Codes require a high standard of evidence for objective weight loss claims, which the Harcombe Diet failed to meet.
In the next post Zoe Harcombe vs the Advertising Standards Authority: Candida (Part 3) I am going to look at claims about Candida overgrowth, food cravings and the dangers of encouraging self diagnosis.
* For clarity, I am not asserting that the diet cannot work, merely considering if the evidence put forward by Zoe Harcombe is robust and supports the claims about weight loss.
** The ‘Calorie Theory’ put forward by Zoe Harcombe is a strawman. ‘Conventional’ weight loss advice does not stand or fall solely on whether a rule of thumb used to estimate the calorie deficit required to lose a given quantity of weight gives a precise and accurate prediction each and every time. Additionally, anyone claiming that the validity of a weight loss model is dependant on its ability to make accurate predictions must, for consistency, also reject alternative theories such as the ‘insulin theory’ which fail this test.
 Draft Recommendation, Advertising Standards Authority, Case Number A13-242778, June 2014