In part 1 of our series we looked at evidence in whether the distribution of protein had an effect on body composition as well as whether breakfast was necessary. Today we look at whether when we eat our food, matters, with a particular focus on when we consume carbohydrates.
No Carbohydrates After 6pm?
Let's face it, who hasn't heard of this ironclad rule for dieting success?
The rationale behind not having carbohydrates in the evening and concentrating them during the day makes sense. When we wake up our bodies haven't had any nutrients for 8-10 hours depending on how long we sleep and don't raid the kitchen fridge during the middle of the night. Protein synthesis (the construction of new muscle tissue) will be downgraded and muscle breakdown will become high. In addition, the stress hormone cortisol will be elevated during the morning and high cortisol levels cause muscle loss as every gym rat knows. Finally, by filling our bodies full of carbohydrates in the morning, when insulin sensitivity is highest, we can use the carbohydrates as fuel to power physical and cognitive activity (remember the brain relies in glucose as a fuel source). The flip side of this argument is that at night we are less insulin sensitive and with us soon to hit our beds there is little to no physical activity we require carbohydrates for (bedroom gymnastics being an exception for any sexaholics reading this).
This rationale makes a lot of sense doesn't it, but does it hold up in fact?
This particular law of nutrition has been studied in fact. A number of studies (1) (2)(3)(4) have all demonstrated the OPPOSITE of what the fitness industry has promoted for years. Weight loss results show variance with some of the studies showing greater weight loss with morning feeding versus evening feeding but once we look at what matters to athletes we see a clearer picture. Fat oxidation rates were higher in all four studies when most of the calories were ingested at night while preservation of muscle mass, a key concern for bodybuilders was also higher when most of the calories were ingested at night time. How do we square this research with the bulk of fitness people advocating the exact opposite approach (consuming most calories during the day, especially carbohydrates)?
Does evolution provide a clue?
They say success leaves tracks and in the case of the human species, the success of our kind might conceivably have something to do with how our bodies were adapted to their environment. Imagine you are Captain Caveman waking up with Mrs Caveman and looking out over the plains of Earth 10,000 years ago. Do you suppose as you got up and brushed your teeth with sabre tooth tiger, that what you would be doing is settling down to a nice, hearty breakfast of Kelloggs Mammoth Munch?
Hmmm, not likely. Rather you'd be awake and then, with no cereal consumption in the distant past, or refrigeration units around, you'd have to wake up and go out to either hunt, or fish for your first meal of the day. Given this, it makes sense that our bodies would adapt to their environment and ensure they function better according to the meal pattern that their situation requires. Flipping forward to the modern day, if our bodies are used to feeding mainly in the evening (primal man would presumably have a big meal around a campfire several hours after the animals were hunted, skinned, and cooked) then it seems unlikely that we can override this pattern just because it suits food manufacturers to have us eating from the moment we wake up to the moment we fall asleep.
Metabolic rate at night
Surely these studies must be missing some detail that makes them invalid such as being conducted on mainly sedentary types who don't move around much and therefore wouldn't burn the carbs used during the day as efficiently as athletes? It is true that these studies on nutrient ingestion didn't specifically work with athletes but we do have some research(5)(6) comparing metabolic rates during the day and night which puts an interesting slant on things. The research shows that while sleeping metabolic rate declines during the first half of the night then it rises in the second half of the night. Of particular interest, while obese individuals did indeed show a slower metabolic rate at night compared to during the day, lean individuals had a HIGHER sleeping metabolic rate than their resting metabolic rate. To put this in layman's terms, bodybuilders and other athletes will see an increase in their metabolic rate at night. So much for consuming less at night because the body is ready to shut down for the day!
By now you hopefully accept that eating at night doesn't hinder and may, based on the evidence, actually enhance your body composition. However, how many times have you heard the old chestnut that you have better insulin sensitivity in the morning and can better handle carbs then? It is true that the body is more receptive to carbohydrate intake in the AM but is there something else other than the time of the day that can explain this? The answer is yes. The improved glucose control shown in morning versus evening meals is attributable to the fact that having fasted overnight your body is handling the carbohydrate load better. A fairer test would be comparing glucose control and insulin response in someone who didn't eat for eight hours between say 1 and 9pm (mimicking our overnight fast) to someone eating after sleep. Similarly, if we compared the second meal of the day versus one at night we should see the effects of overnight fasting eliminated. If the second meal of the day doesn't show a better glucose and insulin response than the last meal of the day it can safely be concluded that it is the fast, not the time of the day, which accounts for the subsequent improved response seen in breakfast eaters. As it happens we have a study showing just that(7).
A number of fitness authorities who have looked at some of the science behind nutrient consumption such as Borge Fagerli, John Kiefer, and Martin Berkhan have all come up with nutrition program centred around minimising or eliminating carbohydrates in the morning, or in the case of Martin Berkhan, any meal at all. None of these people or their adherents seem to have done badly by dropping calories in the morning so you'd think everybody was on board as research presented in this article and real world results all appear to point in the same direction?
Next week, in Part 3 we will be looking at an exciting new front in nutrition research, exploring how circadian rhythms can affect our bodies.
Read Part 3 Now:
1. Sofer et.al (2001): Greater Weight Loss and Hormonal Changes After 6 Months Diet With Carbohydrates Eaten Mostly at Dinner.
2. Keim et.al (1997): 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
3. Al-Hourani HM, Atoum MF (2007) – Body composition, nutrient intake and physical activity patterns in young women during Ramadan
4. Sensi S, Capani F (1987) – Chronobiological aspects of weight loss in obesity: effects of different meal timing patterns
5. Zhang K, et.al (2002): Sleeping metabolic rate in relation to body mass index and body composition.
6. Meijer G et.al (1992): Sleeping metabolic rate in relation to body composition and the menstrual cycle.
7. Biston P et.al (1996): Diurnal variations in cardiovascular function and glucose regulation in normotensive humans.