As with any diet that is promoted by so called “Nutrition Guru’s” they are reliant on the public’s lack of understanding of how to apply and utilise peer reviewed scientific evidence. By quoting lots of research and throwing in some scientific terminology a lot of diets can start to look like they are based on sound physiological, biochemical and metabolic principles. Carbohydrate (CHO) back-loading is a good example of this misrepresentation of the scientific literature.
Using carbohydrate back-loading as a diet regime.
To look at the science associated with this diet it would be helpful to know what it is. First off you try to eat lightly in morning (this could include skipping breakfast) and early afternoon hours. You can then feast at night on pretty much any type of CHO you fancy. You will have to avoid CHO until after your workout, which (ideally) should be later in the afternoon. For a lot of people training in the evening may not be practical. Ironically given the whole premise of the diet its main author (John Keifer) then explains how to train at different times so already contradicting the main hypothesis? Your main CHO intake begins with your post-workout meal and then continues throughout the evening. The major advocate of this diet is John Keifer and he has no peer reviewed publications based on CHO or CHO back-loading; this may be because one of his degrees is in mathematics? His book mis-quotes scientific literature in places and over-simplifies complex physiological and metabolic processes. This diet is supposed to take advantage of the natural daily fluctuations in insulin sensitivity in muscle and fat cells, as well as the exercise-induced increase in insulin sensitivity in muscle cells. These fluctuations occur as part of your circadian rhythm. The study quoted to support this1 does show that hormones shift with circadian rhythm but doesn’t discuss fat storage and utilisation. The principle hypothesis with CHO back-loading is that you use the fluctuations to your advantage by not eating CHO when your body is most able to store them as fat (early in the day). Instead, you eat CHO when your body is most likely to store them as glycogen in the muscles (later in the day, after working out).
Does this diet work?
Well the first thing to highlight here is that there have been NO Randomised Controlled Trials (RCT’s) showing that CHO back-loading is effective. This is very relevant as RCT’s are considered the gold standard when it comes to establishing scientific fact in human populations. Within the CHO back-loading literature itself numerous studies have been quoted to support the theory. However the two most quoted and used extensively are really not that strong in terms of scientific evidence. The first study2 quoted regularly included only ten female subjects in total (split into groups of 6 and 4). In terms of scientific evidence this is at best a pilot study and you could only apply finding to females and that would be streching the validity somewhat. In this study the participants who ate larger morning meals produced more weight loss. However, with larger afternoon meals fat free mass was protected (but not increased). An interesting aside here is that in his book Keifer suggests lean tissue increased and quotes this particular study, it did not increase? The second study that forms a cornerstone of evidence for CHO back-loading was published in Obesity3, in this study 78 obese men were studied (BMI >30), so again the findings from this could only be applied to obese males. Given that this diet is often promoted as the way for people training regularly to reduce their body fat the two populations studied don’t really fit that demographic? In this second study the dietary intake was self-reported (this is inherently inaccurate). After six months the weight loss was only 5lbs greater in the group eating more CHO in the evening; this is not significant weight loss. Subjects reported consuming 0.66 to 0.76g protein/kg BW, just about enough to sustain lean tissue but not with a kcal deficit so the protein intake was too low and as this was self-reported it is debatable how accurate this data is. As subjects were on a low kcal intake you would expect fat loss. Finally the main premise of CHO back-loading is to eat CHO post workout; these subjects were not exercising. Again this is at best evidence for some effect in obese males who don’t exercise. Not exactly the average personal training client or gym attendee?
Numerous reviews of dietary meal timing and macronutrient manipulation have failed to support the overall hypothesis of CHO back-loading4, 5, 6 these are a few examples. In a recent scientific review of nutrient timing by Aragon and Schoenfeld (2013)7 came to the following conclusion:
“For the goal of maximizing rates of muscle gain, these findings support the broader objective of meeting total daily carbohydrate need instead of specifically timing its constituent doses. Collectively, these data indicate an increased potential for dietary flexibility while maintaining the pursuit of optimal timing”.
This type of scientific review takes all the latest evidence and then statistically analyses it to see if there are any particular trends or inferences that can be drawn. This current review supports the view that macronutrient timing overall is not as critical as meeting your daily requirements. There will be the odd person for whom eating CHO later in the day may be beneficial much as eating CHO early in the day will be beneficial for someone else. Diet is very individual and to claim that one system fits all fly’s in the face of the current scientific evidence. CHO back-loading meets all the criteria for being classified as a FAD diet and is certainly not based on sound scientific evidence as I have demonstrated here, I hope.
If you would like further nutrition and weight loss tips why not sign up for the FREE seven video series by completing the simple form below?
- Molecular & Cellular Endocrinology. 2012 Feb 5;349(1):91-104
- Journal Nutrition. 1997 Jan;127(1):75-82.
- Obesity, 2011 Oct;19(10):2006-14.
- Journal of the International Society of Sports Nutrition. (2013), 10:5.
- American J Clinical Nutrition. 1992 Mar;55(3):645-51
- Chronobiology Int. 1987;4(2):251-61
- Nutrition. 2007 May;23(5):385-91.