‘Critical differences’ between Virta and Gardner studies — Noakes

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NoakesA ‘critical difference’ between the Virta and Gardner studies was that the food intake of the subjects in the latter study was self reported, which is ‘notoriously inaccurate’, writes Prof Tim Noakes in response to a letter last week from Ms Ingrid Schloss, dietician.

Professor Tim Noakes responds to a letter from Ms Ingrid Schloss.

He writes:

In response to the letter from dietitian Ms Ingrid Schloss, it is important to make the point that there were two critical difference between the study she quotes (Gardner et al 2018) and the Virta Health study. In the Virta Health study the compliance of the research subjects to the imposed diet was monitored essentially on a daily basis through the measurement of the metabolic effects of food intakes on blood glucose and ketone concentrations. This did not happen in the Gardner et al study. Thus, we cannot be absolutely certain of exactly what it was that subjects in that study ate since self-reporting of diet is notoriously inaccurate.

But more importantly the Virta Health study specifically studied the effects of very strict carbohydrate restriction (<30g carbohydrate/day) whereas the Gardner et al study used a much more liberal carbohydrate intake (>130g carbohydrate/day) in the so-called low carbohydrate diet group. Many of us would not consider a diet providing 130g carbohydrate/day as a low carbohydrate diet as clinical experience shows that those with the more severe insulin resistance will show a substantially superior metabolic response to carbohydrate intakes below 30g/day than at >130g/day. That in essence is what the Virta Health study shows: For those patients with insulin resistance/T2DM and those practitioners who wish to reduce their patients’ reliance on insulin and other medications to manage their condition, the message from the Virta Health study is that the only proven diet that offers the best probability for success is one providing less than 30g carbohydrate/day.

It is perhaps rather unfortunate that Ms Schloss failed to emphasise that point since until dietitians and clinicians begin to prescribe very restrictive carbohydrate diets for patients with T2DM, those patients will continue to receive sub-optimal care (as clearly shown by the Virta Health study).

Ms Schloss’s letter exposes one other important point. When the low carbohydrate diet was first promoted in South Africa after the publication of The Real Meal Revolution, the almost unanimous outcry from the medical and dietetics professions (as we describe in Lore of Nutrition) was that this diet is dangerous and will lead to epidemics of coronary artery disease and cancer and all the complications of those disease. Now with the publication of the Gardner et al and Virta Health studies (and many others), Ms Schloss is reduced to arguing that actually the low-fat diet is just as effective as the so-called low carbohydrate diet for weight loss. No longer is the argument that the low carbohydrate diet is inherently dangerous. This is a fundamental and not so subtle shift from the previous agenda which was to vilify the low carbohydrate diet and any who promote it.

My trial before the Health Professionals Council of SA (HPCSA) was the most obvious example of that targeted vilification.

Professor Timothy Noakes
The Noakes Foundation, Cape Town


JAMA abstract
Virta Health Study

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