In the latest Lancet, Yoni Freedhoff and Kevin Hall have an opinion piece about diet trials, in which they argue that it’s not helpful to know that an ad lib low-carb diet results in more weight loss than a calorie-restricted low-fat “dietary guidelines” type diet, because the weight loss differences are not clinically significant, a claim which we think is both false, and overlooking other benefits of carbohydrate restriction.
They then go on to ask that more effort go into identifying ways to ensure that people can adhere to diets long term, a reasonable request and something we’re very much interested in ourselves. However, they spoil this a bit by talking about “hype” (short for hyperbole) and “society’s endless parade of fad diets”. If you want to improve adherence to diets and you think that there is little to choose between them, why use the word “fad”, which is normally used to devalue people’s dietary choices?
Further, is there even an endless parade of diets these days? Aren’t there a just few variations on and recombinations of the same timeless themes, such as vegan or vegetarianism, calorie restriction, carbohydrate restriction, ancestral, and so on? The only really original idea is fasting, yet this ancient therapy only seems original because we’ve just been led through such an intensive era of round-the-clock eating.
Freedhoff and Hall concentrate their argument on one trial, the DIRECT study (sometimes better known as Shai et al.) which was a 24-month workplace intervention in Israel, with ad lib low-carb, low-fat calorie restricted, and Mediterranean diet calorie restricted arms. “The low-carbohydrate, non–restricted-calorie diet aimed to provide 20 g of carbohydrates per day for the 2-month induction phase and immediately after religious holidays, with a gradual increase to a maximum of 120 g per day to maintain the weight loss…the [low carb] participants were counseled to choose vegetarian sources of fat and protein and to avoid trans fat. The diet was based on the Atkins diet.” The Mediterranean diet (at 40% fat, mainly from olive oil and nuts) was based on a 2001 book by Walter Willett and PJ Skerrett, and the low-fat diet was based on American Heart Association dietary guidelines. All dieters had access to the same food in the workplace cafeteria, but the food suitable for each different diet was colour coded.
In this study, people in the low carb group (not very low carb after induction, it varied between 87g/day at 6 months and 120g/day reported CHO intake over the first 12 months) lost on average 1.8 Kg more weight than the low fat dieters overall.
Well as Freedhoff and Hall say, that’s not a lot of weight in the grand scheme of things. So does it support their claim that we should stop caring about the results of these studies?
Not so fast. The average weight loss includes all the people who drop out of the study; this is “intention to treat” (ITT) analysis, designed to keep the randomisation of baseline characteristics stable.
But what you might want to know if you were choosing a weight-loss diet, is, what will happen to me if I follow the diet? There were more drop-outs (22% vs 10%) in this study in the low carb arm, who found it hard to resist the biscuits and cakes in the cafeteria (interestingly, this caused their intake of saturated fat to increase over the study, even as their total fat intake went down), and self-reported complete adherence to low-carb was 57% at month 24. The superiority of the low carb diet in DIRECT includes the effect of including this higher drop-out rate, and those extra cakes and biscuits. The per-protocol analysis only gives us a stratified comparison of completers vs non-completers (i.e. minus drop-outs, but including those with weak adherence to diets) at 24 months, but we do know from other studies that when non-completers are excluded, the long-term difference between diets at 12 months becomes larger.
So compliance is important, sticking to the diet is critical of course, but what diet you stick to matters more than Freedhoff and Hall are saying. In the DIRECT study, people who completed 24 months of the low-carb diet lost a mean 5.5 +/- 7.0 Kg, and those who completed the low fat diet lost 3.3 +/- 4.1 Kg. The biggest loser in the DIRECT study lost 35% of their body weight, but all we know about the most successful dieters is, that they weighed more at baseline, lost weight more rapidly in the early stages, and ate a bit less protein and cholesterol at baseline (but overall the protein intakes in this population were, and remained, quite high). Rapid weight loss early in a diet is usually associated with success, and of course it’s a feature of the ketogenic diet, or the induction phase of the Atkins diet here.
But wait, there’s more. Weight loss isn’t the only effect of diet, and overweight people often suffer from increased cardiometabolic risk owing to insulin resistance and the metabolic syndrome.
Freedhoff and Hall for some reason don’t mention this, but it’s the evidence we have about the “long term safety” of any diet. In all parameters the ad lib low carb diet does better than the calorie-restricted low-fat diet, even at 24 months, and even including the drop-outs.
“Among the participants with diabetes, the proportion of glycated hemoglobin at 24 months decreased by 0.4±1.3% in the low-fat group, 0.5±1.1% in the Mediterranean-diet group, and 0.9±0.8% in the low-carbohydrate group. The changes were significant (P<0.05) only in the low-carbohydrate group (P=0.45 for the comparison among groups).” In fact, as far as we know, carbohydrate-restricted diets are the only diets that can produce some of these benefits without weight loss.
There’s a curious extra point in the chart below – LDL rose slightly at 6 months in the low-carb arm, when adherence was good and polyunsaturated fat intake was high, and dropped at 24 months when polyunsaturated fat intake decreased and carbohydrate, but also saturated fat, intake increased.
But wait, there’s more. Something else that Hall and Freedhoff didn’t mention is the very long-term effects of this diet trial, because there was a four-year follow-up study. And the results here are very interesting, because there is less of a rebound effect for the ad lib low carb diet and the Mediterranean diet than for the low-fat, calorie restricted AHA diet.
In the low-fat diet group (which had the fewest drop-outs) most of the improved metabolic parameters, including weight, are back to baseline levels. In the low-carb group, weight and the LDL/HDL cholesterol ratio are still improved. This is four years after the end of a 2-year study – six years in all. Quite a different result from Hall’s Biggest Loser study, where severe rebound weight gain from CICO “eat less move more” energy restriction was the order of the day.
After the completion of intervention, the participants were invited once a year to the clinic for a regular check-up and were encouraged to pursue a healthy diet. Although diet-group color coding and nutrition labeling in the workplace cafeteria were stopped at the end of the intervention, the cafeteria continued to serve suitable meals according to the guidelines of the 3 diets, suggesting that the workers could still consume their specific dishes, which continued to be regularly served, as they were during the trial. We did not continue with the dietary sessions or any other activity encouraging adherence. We used one question: Are you still dieting? The question had three possible answers to choose from: 1. “Yes, with my original diet” 2. “Yes, but I switched to another diet” 3. “No, I am not dieting”. No differences were observed in response to this question between the 3 assigned diet groups (p=0.36).
Perhaps there are a few people in this group who were so happy with their results that they stuck with the low-carb diet for 6 years, and their results are carrying the rest – or perhaps the 2 years of low-carb diet (or the 2 months of ketogenic dieting) had lasting benefits. These questions weren’t really answered by the questionnaire quoted above, which kind of refutes Freedhoff and Hall’s suggestion that we have nothing more to learn from diet comparisons. Good post hoc analysis of the data from weight loss trials can seek to develop further hypotheses about what baseline markers, characteristics, and responses predict success, and that should inform the design of further trials and interventions. It’s also possible to tweak the diets to improve them for both effect and ease of compliance – (e.g. what if the AHA diet had been lower-GI, the Med diet lower carb, and the low-carb diet lower carb, with more Mediterranean and real food elements? Something like this probably went on during the 4-year follow-up among the people still interested in the diets).
But in the meantime, we needn’t let ourselves get confused about how to proceed.
As Prof Richard Feinman says, “remind me again why we have a medical science literature?” Comparative trials of diets and drugs are designed and published so that we know what is the most effective option between two or more choices for any given diagnosis. The intention is that the best treatment, determined by experiment, will be the one to be offered first. The patient may not like it, or it may not work, in which case it will be time to try something else, but the evidence is there to inform the discussion.
Instead we are stuck in this Catch 22 where the evidence about the best treatment for overweight and diabetes, collected over decades at great expense, is ignored (or worse) because its results contradict cherished beliefs about (in this case) the pre-eminence and equivalence of the calorie, or (at other times) the health effects of saturated fat.
Fortunately some people are brave enough to follow the existing evidence while applying themselves to solving the question of adherence. David Unwin and colleagues in the UK have worked on the psychological aspects of motivating and supporting people in low carb diets for type 2 diabetes and NAFLD with great success, and recently a multicenter LCHF approach in Canada has also reported good adherence and impressive results.
A thought experiment
The DIRECT study had no control group, i.e. no group of people from the same population eating a normal (whatever they are normally eating) diet ad lib.
Imagine there was a fourth arm randomised to an ad lib version of one of the 3 diets.
Without calorie restriction, it seems less likely that the AHA-approved, last-year’s dietary guidelines diet would have made any difference from baseline. It’s possible that nothing would have improved and plausible that things would have continued to get worse overall.
Without calorie restriction, it’s likely that the Mediterranean diet (the modern, updated dietary guidelines diet) would still have been better than the AHA-approved, last-year’s model dietary guidelines diet.There may well have been some smaller improvements, and things would be unlikely to get worse.
Now imagine an ad lib version of the LCHF diet (the controversial, alternative-dietary guidelines diet). The results would still be exactly the same, because the experimental diet was ad lib.
 Freedhoff Y, Hall KD. Weight loss diet studies: we need help not hype. The Lancet , Volume 388 , Issue 10047 , 849 – 851.
 Shai, I, Schwarzfuchs, D, Henkin, Y et al. Weight loss with a low-carbohydrate, Mediterranean, or low-fat diet. N Engl J Med. 2008; 359: 229–241
 Greenberg, I, Stampfer, MJ, Schwarzfuchs, D, and Shai, I. Adherence and success in long-term weight loss diets: the dietary intervention randomized controlled trial (DIRECT). J Am Coll Nutr. 2009; 28: 159–168
 Feinman RD. Intention-to-treat. What is the question? Nutr Metab (Lond). 2009 Jan 9;6:1. doi: 10.1186/1743-7075-6-1. Full text:
 Gannon MC, Nuttall FQ. Control of blood glucose in type 2 diabetes without weight loss by modification of diet composition. Nutrition & Metabolism 2006 3:16 DOI: 10.1186/1743-7075-3-16. Full text:
 Schwarzfuchs D, Golan R, Shai I. Four-year follow-up after two-year dietary interventions. N Engl J Med. 2012 Oct 4;367(14):1373-4. doi: 10.1056/NEJMc1204792.
Full text: http://www.nejm.org/doi/full/10.1056/NEJMc1204792
 Fothergill, E, Guo, J, Howard, L et al. Persistent metabolic adaptation 6 years after “The Biggest Loser” competition. Obesity (Silver Spring). 2016; DOI: http://dx.doi.org/10.1002/oby.21538 (published online May 2.)
 Unwin DJ, Cuthbertson DJ, Feinman R, Sprung VS (2015) A pilot study to explore the role of a low-carbohydrate intervention to improve GGT levels and HbA1c. Diabesity in Practice 4: 102–8. Full text:
 Mark S, Du Toit S, Noakes TD, Nordli K, Coetzee D, Makin M, Van der Spuy S, Frey J, Wortman J. A successful lifestyle intervention model replicated in diverse clinical settings. S Afr Med J. 2016 Jul 3;106(8):763-6. doi: 10.7196/SAMJ.2016.v106i8.10136.
full text: http://samj.org.za/index.php/samj/article/view/10136/7528