Monday, September 1, 2014

Should We Be Eating Our Carbs at Dinner? A Recent Study Seems to Suggest Just That, But Close Analysis Reveals: Balanced Meals Increase Fat Loss, Esp. from the Trunk

Time for carbs, or time for protein? Not really a useful question, as a closer analysis of a recent study shows.
Members of the ISSN Facebook group may already have read my comments on a recent study from the Federal University of Vicosa in Brazil (Alves. 2014). For someone like Lawerence who posted a link to the study in said Facebook group and who doesn't have access to the full-text article, the study apparently suggests that you "should be eating your carbs at dinner" (see his comment).

Why? Well, the conclusion of the study, which investigated the effects of macronutrient timing on on body weight and composition, energy metabolism, and biochemical markers in overweight/obese men, speaks of increased dietary thermogenesis of eating carbs at night and a negative impact of eating protein mostly at dinner and carbohydrates at lunch on glucose management.
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What is actually interesting is not what happened, when the scientists messed with the diets of their 18-45 year-old subjects with body mass indexes ranging from chubby 26kg/m² to obese 35 kg/m² and stable weight (±3 kg) during the previous 3 months, though. What is interesting is what happened, when they were eating mixed meals like any sane individual that has not been infected by the Internet "macronutrient timing" virus.
Figure 1: Detailed breakdown of the macronutrient composition of lunch and dinner in the three intervention group; relative energy and total macronutrient content were identical (Alves. 2014)
While all diets contained the "exact" same amount of nutrients (18% of the calories from protein, 30% from fat and 52 % from carbohydrate; 1.2g/kg protein) and energy (10% below maintenance diet; ~250kcal energy deficit) the overview in Figure 1 tells you that the macronurients were distributed differently across a 24h period in the CONTROL, DCNP and DPNC groups. With carbohydrates mostly at lunch and protein mostly at night in the DCNP, and protein at lunch and carbohydrates at night in the DPCN group.

Don't fall for what the abstract suggests

Now the initially mentioned conclusion in the abstract on pubmed and elsewhere suggests that it would be beneficial to postpone your carbohydrate intake to the evening hours. I mean, an increase in DIT (=dietary thermogenesis) sounds great and the absence of the nasty ups and downs of the glucose metabolism in the DPNC group certainly ain't bad, either. So why shouldn't we eat all our protein at lunch and the carbs at night?

Well, the reason is easy. The abstract does not mention the most important observation: The fact that the control diet was superior in the practically all relevant study outcomes. So, the increase in DIT as nice as it may sound - What is it worth, if it does not translate in increased fat loss?
Figure 2: Changes in body composition and glucose & lipid management (Alves. 2014)
If you take a look at the data in Figure 2, you will realize that the improvements dieters will usually look for, i.e. decreases in fat mass, and especially trunk fat, were (non-significantly) more pronounced in the control than in any of the two "nutrient timing" groups. In view of the fact that the same goes for the improvements in glucose and lipid management ain't an argument in favor of "having all your carbs in the evening either - even if the only significant difference were for insulin and HOMA-IR (compared to the DCNP group).
Bottom line: As fancy as it may sound, the whole macronutrient timing shenanigan eventually doesn't provide measurable advantages over the allegedly boring, but simple and effective consumption of balanced meals. When all is said and done, it's rather quite the opposite.

The role of insulin as a metabolic Zeitgeber would be another argument against having all your carbs in the evening ... well unless you are about to travel across time zones and want to avoid feeling jet lagged | learn more.
Nevertheless, if we take another look at the data, we will have to admit that there is one advantage to having all your protein in the evening: A reduced loss of lean mass (should remind you of having a slow digesting protein pre-bed | learn more).

Whether this ~1/2 lbs difference in lean mass loss is something that warrants a reduction in fat loss, messed up HBA1C and insulin levels and reduced improvements in lipid management is yet as questionable, as the the general notion that "we should be eating our carbs at dinner." A hypothesis that seems all the more unlikely in view of the recently elucidated role of insulin as a metabolic clock zeitgeber that would suggest to eat carbs in the morning | Comment on Facebook.
  • Alves, Raquel Duarte Moreira, et al. "Eating carbohydrate mostly at lunch and protein mostly at dinner within a covert hypocaloric diet influences morning glucose homeostasis in overweight/obese men." European journal of nutrition 53.1 (2014): 49-60.