This article will assess the validity of the claims made in the carb backloading (CBL)book to determine if it is the ultimate diet. Firstly, I will give a very brief summary about how CBL works. The basic plan is to have an introductory low carb phase (10 days) to increase insulin sensitivity. (The amount of weight lost can be used to determine maximum amount of carbs for training days) Once the actual CBL plan starts, it is recommended to eat only protein and fats during the day (and some residual carbs from fibrous vegetables are ok), afternoon resistance training session, then consume protein and carbs and then “feasting” on specifically high GI carbs. For more on GI see this article.
The introduction of the book is alluding to the fact that specific carb timing can “gain muscle and lose fat at the same time”. This is the ultimate goal of many gym goers but unfortunately there are very few instances where this actually happens. Typically these are A) for beginners to resistance training B) people that have previously trained and have “muscle memory” C) people that are using anabolic steroids. So how does CBL do this? Let’s take a look. “Eat breakfast like a king, lunch like a prince and dinner like a pauper” is a common term used in nutrition circles. Kiefer explains that this has never been proven by science as all of the studies have been correlation not causation. I totally agree with this.
“Modulated Tissue Response is the ability to select which tissues grow and which shrink e.g. growing muscle while losing fat” This chapter explains some of the anabolic and catabolic reactions to different hormones and specifically that cortisol can be catabolic for fat tissue while being anabolic for muscle tissue at the same time. Apparently, if you can customise your dietary needs to your specific goals you can “look like a superhero”. The following chapter is a layman’s guide to insulin which stems from the old “good calories bad calories” tripe and evolves into “don’t think you need super elevated levels of insulin 24/7”. Fails to mention that protein is also insulinogenic.(1) It then goes on to say that insulin sensitivity is high in the morning and lower at night. (2) However, this study was done on people who have been diagnosed with non-insulin-dependent diabetes mellitus. The body is insulin RESISTANT in the morning (known as the “dawn phenomenon”), which means it is LESS capable of quickly storing excess glucose. So, no, your fat cells won’t “soak up sugar like a fat kid with a gallon of melted ice cream and a straw” as the book states- quite the opposite. The basic premise is that we should reduce carbs during the day as insulin sensitivity is supposedly higher and we are more predisposed to storing fat. As was said earlier, this neglects the fact that protein is also insulinogenic. Another important point is that if the person had completed an effective resistance training bout within the last 24 hours, the nutrient partioning likely to be favoured towards muscle tissue rather than fat as studies show that the post work out “anabolic window” is closer to 24hrs.
5 studies are cites as proof that people who skip breakfast and eat after 7pm lose body fat and may actually gain muscle. The first study was done on 10 women over 12 weeks and concluded that (3) “ingestion of larger AM meals resulted in slightly greater weight loss, but ingestion of larger PM meals resulted in better maintenance of fat-free mass. Thus, incorporation of larger PM meals in a weight loss regimen may be important in minimizing the loss of fat-free mass.” There is no mention of any specific exercise in this study. The primary study on this topic was done by Sofer et al which compared the effects of carbs eaten mostly at dinner versus spread throughout the day. The results were promising for night time carb consumers as this group achieved greater weight loss, waist girth reduction, body fat reduction as well as improved glucose control, inflammation reduction, lipid profile and satiety levels. This is all looking great but how well does this apply to the athletic community? The participants were Israeli Police offices with an average weight of 98.3kg who were placed on a 1300-1500kcal diet. The prescribed diet was 20% protein, 40-50% carbs and 30-35% fat. If the participants were 100% accurate with their dietary records this leaves us with 65-75g of protein per day which is not even enough to be optimal for most small women. This equates to .66-.76g/kg which is well below the scientifically tested optimal rates. See here The relevance of this study is minimal to the athletic population who typically consume closer to 2g/kg of body weight or more and are not (or should not) be on diets with calories set at approximately 6.5kcals per lb of body weight. See what happens here.
The other aspect of CBL is non-insulin mediated glucose transport into muscle cells. The theory is that post exericse, you can ingest large amounts of carbohydrates and the muscle tissue will take up a huge amount of it before insulin is released and thus will not be taking up by fat cells. The issue with this is that when exercising the body is burning glycogen (even small amounts during LISS cardio but higher during resistance training). In response to the use of glycogen stores by the muscles, the body releases small amounts from your liver as glucose and dumps it into the bloodstream, with the goal of getting this sugar to the working muscles. Because of the high intensity activity, the body will allow the glucose that has been released from the liver to be taken in by muscle tissue to restore glycogen levels. (Once again the studies cited were done on diabetics) For non -diabetics, within seconds of ingesting carbs, the body will release insulin and it does not matter what time of day it is or if you are pre/post workout. The amount of insulin released is based on having high levels of blood glucose and it’s own pulses during the day. (dawn phenomenon.) If the theory was correct, there would be a clinically insignificant amount of additional glucose taken up by muscle tissue as even with resistance training the amount of glycogen depletion is minimal. (a few grams typically) So the muscle tissue cells are replenished and the surplus goes straight to the fat cells. (not necessarily to be stored)
In summary, CBL has taken a lot of studies that have dealt with selective criteria and attempted to apply them to a very complex system. If the premise behind the diet was that it would make you less hungry during the day and will lose weight then that would be applicable. (assuming calorie deficit) But as the basis is that you can selectively gain muscle while losing fat, this is far fetched. Overall, there MAY be some benefits from this style of eating but there is currently no science to conclusively back this up. Once again, the primary factor in weight loss/gain is energy balance. If you have this down pat and would like to try a CBL diet with the same macronutrient totals, then go ahead. There is a possibility that it could be beneficial. If this is a significant difference is yet to be seen. As always, I recommend choosing the meal (and macronutrient) frequency that you can personally comply with over time. If you love your morning oats and toast and it fits into your macronutrient goals, then I wouldn’t be giving that up to try this “just because”.
The best diet is the one that you can adhere to over time.
- Salehi A, Gunnerud U, Muhammed SJ, Ostman E, Holst JJ, Björck I, Rorsman P. The insulinogenic effect of whey protein is partially mediated by a direct effect of amino acids and GIP on beta-cells. Nutr Metab (Lond). 2012 May 30;9(1):48.
- Gautier JF, Cathelineau G. Insulin sensitivity and hepatic glucose production: nycthemeral variations. Diabetes Metab. 1997 Nov;23 Suppl 4:35-8.
- Keim NL, Van Loan MD, Horn WF, Barbieri TF, Mayclin PL. Weight loss is greater with consumption of large morning meals and fat-free mass is preserved with large evening meals in women on a controlled weight reduction regimen. J Nutr. 1997 Jan;127(1):75- 82.