Greater weight loss and hormonal changes after 6 months diet with carbohydrates eaten mostly at dinner.
Today’s review actually ties in quite nicely with my first post about fat gain and carbohydrates and the myths that surround them. A lot of fitness enthusiasts are, what I like to call, “Carbophobics,” meaning that they fear carbohydrates and/or sugars. This is, in part, due to a gross misunderstanding of how insulin works in the body and how it stores carbohydrate. For this reason alone some extremists severely limit their carb intake for fear of fat gain, while others limit sugars (which are wrongly perceived as having a greater affinity to be stored as fat), and a good handful of people even go so far as to forbid carbs past some arbitrary time of day. This typically occurs sometime in the late afternoon/early evening, which segues nicely into today’s topic.
As you may have already read (skimmed?), the article that I will be speaking about involves carbohydrates and weight loss, but more specifically, carbohydrates being consumed at dinner time causing greater weight loss than carbohydrates spread throughout the day. This is a relatively novel concept in terms of a structured weight loss diet, however, a similar diet plan has been studied before, mainly in Muslim populations which participate in Ramadan, a month-long religious observation where people refrain from food and drink during daylight hours and then consume some form of enriched-carbohydrate dinner at night. Along a similar vein, the researchers of this article discuss how manipulating carbohydrate intake during a hypocaloric diet might have greater beneficial effects on obesity, certain metabolic markers associated with diabetes (insulin sensitivity, fasting glucose, lipid profile), and overall satiety than does a traditional low-calorie diet where carbs are spread out over the course of the day (breakfast, lunch, dinner).
Their rationale is based on eating in accordance with the natural diurnal (daytime) rhythms of certain hormones in the body (namely insulin, leptin, and adiponectin) which deal with metabolism, hunger and satiety. I won’t go into too much detail, but in theory, if you can control the way these hormones act on your body throughout the day you can curb your hunger and lose more weight and essentially adhere to a diet more so than someone who is fighting their hormonal physiology on a standard diet. In this manner, you can diet longer and lose even more weight… hypothetically. This is exactly what this study sought to examine. Sounds good, right? Well, some of you out there might not buy it at all (carbophobes), while others may take it for gospel and eliminate their daytime carbs right off the bat. I, on the other hand, would rather take a more sound/sensible approach and see how they conducted this study before I go jumping to conclusions.
The study was conducted in Israel with a cohort of 78 relatively healthy police officers, between the ages of 25-55, and who had a BMI > 30 (overweight). 39 officers were randomly assigned to the control group (i.e. carbs throughout the day), while the remaining 39 officers were part of the experimental group (i.e. carbs for dinner). Randomization essentially eliminates any differences seen between the groups and makes them equal across all variables. From this any results can be seen as a direct relation to the experimental procedure.
The researchers (unlike the last study I talked about) controlled for calories, so that each group received the same amount of calories (1,300-1,500kcals/person) as well as macronutrient composition (20% protein, 30-35% fats, and 45-50% carbohydrates). This amounted to roughly 65-75g protein, 43-50g fats, and 163-188g carbohydrate for each group participant. The participants also filled out forms, periodically throughout the study, which ranked their hunger and satiety on a scale from 1-10, 1 being starving and 10 being devastatingly full. Finally, researchers took blood samples (also periodically throughout the study) to measure certain health markers such as insulin resistance and fasting glucose (which are indicative of metabolic syndrome and diabetes), as well as lipid profile (cholesterol, and triglycerides) and certain hormones (leptin and adiponectin, which are known to regulate hunger and satiety). This was all done at day 0 (baseline), day 7, day 90, and finally at day 180. The participants were also met by a personal dietitian every 1-3 weeks to make sure the diet was adhered to. Those who failed to comply with the diet were thrown out of the study.
By the end of the study the researchers saw that both groups lost significant amounts of weight and both improved upon their health markers, however, the group who received the majority of their carbohydrates at dinner lost more weight and had better health markers than the group who ate carbs throughout the day. Most notably, the experimental group had lower insulin concentrations and lower fasting glucose levels, (meaning they were moving farther away from becoming diabetic). They also improved upon their levels of adiponectin, a hormone which is involved in lowering insulin levels. Probably the most important finding of the study was that the group who received their carbs later in the day reported feeling less hungry and more satiated than the control group. In fact, the experimental group actually felt FULLER as study went on, while the control group got hungrier over the 6 month period. If you’ve ever tried to lose weight for any significant period of time you know that this usually is NOT the case. Even more interesting was the finding that not one of the experimental group participants had preoccupied thoughts about food, whereas one-third of the control group did by 6 months. Again, this is something else not common during dieting.
So, what can explain these results? The researchers believe, as I pointed out in the beginning, that by eating in accordance with the natural diurnal rhythms of certain hormones in the body, one can actually take advantage of these hormonal “windows of opportunity” and curb appetite while losing more weight. This is, in part, due to being able to keep leptin elevated during the day, telling the brain not to eat and to increase energy expenditure. However, as measured through blood sampling, leptin concentrations weren’t much different between the two groups throughout the study, so it is hard to explain why the experimental group felt fuller and was more satiated at 6 months.
The other question, as to why the experimental group became less insulin resistant than the control group, could be explained by the experimental diet keeping insulin release lower throughout the day, allowing adiponectin concentrations to be higher than the control group’s levels. As the authors point out, when insulin is high adiponectin is low, therefore negating the effects of adiponectin. Adiponectin is known to play a role in energy metabolism, specifically with carbs and fats, and helps to lower these concentrations in the body, causing one to be less insulin resistant (i.e. not diabetic). As seen with blood sampling, the experimental group’s concentrations of adiponectin were much higher than the control groups’ levels, possibly explaining the reason for having better insulin and fasting glucose levels.
So, would I go so far as to say that everyone should consume carbs at night rather than throughout the day? Well, maybe if you’re dieting and have had problems adhering to diets in the past. The evidence seems to suggest better satiety which may help you to eek out a couple more weeks or so of dieting. Also, most people like to go out with friends to dinner, so going carb-free throughout the day and saving your carbs for the evening may be more realistic and help you better adhere to your diet when faced with social gatherings. Personally, I would have liked to have seen the study completed up to 1 year. Many studies see very different results in diet protocols past the 6 month point, so it’s hard to say what would happen in the long-run. Also, I wish there was a third and fourth group with a carb-load in the morning only and carb-load at lunch only. Perhaps it doesn’t matter when the carbs are being consumed as long as it only happens once throughout the day?
If you’re overweight or obese and are looking to improve insulin sensitivity, this diet might be a better approach than a traditional weight loss diet. However, exercise has a strong effect on insulin sensitivity, so a traditional diet coupled with a solid exercise plan may be just as good. This was something not talked about by the authors. My thoughts are that this is a great study with a novel approach to losing weight, however, more studies need to be done in order to confirm or deny that dinner is ONLY time in which the carbs can be consumed to yield this result. So for now, as long as you’re healthy and you’re exercising and eating correctly I see no need to eat your carbs at dinner-time only.