I think alot about conventional wisdom and where it may have come from.
Things like “Breakfast is the most important meal of the day.” and “Don’t eat too close to bedtime.”
Many people dismiss these things in favor of trying to trick the body by skipping breakfast but this usually just means they eat later in the day. I tend to think, like many traditional things, these statements are based in a deep truth and an intuitive insight into human physiology.
Both of these statements make me think about how our hormones work at various times of the day. Things like insulin sensitivity and cortisol patterns come to mind.
This study discusses diurnal variations in insulin resistance. While they are able to measure that we are less insulin sensitive in the evening, it isolates two possible reasons and cannot determine which it is.
Diurnal Variation in Insulin Sensitivity
It is the opinion of the researchers that it could be either the expression of clock genes in muscles that increase fatty acid metabolism and reduce the need for glucose in muscles (peripheral insulin resistance) or the increased level of FFA (Free Fatty Acids) in blood later in the evening.
I can totally buy into the clock genes theory as you can see that we have many internal clocks that guide the way we react to and secrete various hormones. What I don’t buy is the idea that the higher level of FFA in the blood is causal. Yes there are more FFA available because the subjects were eating fat throughout the day. Of course. Just because there are FFAs at the scene it does not make them the perpetrators of the crime. Just like fire fighters being at a fire does not mean that they are starting the fires. It is more likely that the muscles become insulin resistant at night for good reason and not as a result of eating all that naughty fat. All 30% of it. It would only make good sense that if the muscles are happy using fatty acids for fuel and glucose is better used elsewhere, like in the brain and red blood cells, that the body would be smart enough to regulate it’s fuel partitioning to be most efficient.
Also the difference in FFA available right before breakfast was barely different from right before dinner.
0.68 μmol/mL before Dinner
0.52 μmol/mL before Breakfast
This is literally nothing. It is like saying a pool is more full after putting a drop of water in it. Of course it is technically more full but does this make any meaningful or measurable difference? Nope. This is reaching for something that is not there.
The graphs of FFAs in this study do show an interesting thing. Almost immediately after eating a meal of 55% of total energy as carbohydrates, 15% as protein, and 30% as fat, the availability of fatty acids as a fuel drop like a stone. This demonstrates the power of insulin to clear fatty acids from the blood as an available fuel source. They also appear to stay low for at least 4 hours after a meal when you eat this way. Essentially if you are eating every 4 hours and you are eating that level of carbohydrate, you will never be able to utilize fat as fuel. No wonder people are getting fatter and fatter.
I believe that there is an alternate reason for why we move towards insulin resistance at night. If we think back to hunter gatherer ancestors, they would not have a whole lot of excess adipose tissue available. If they needed to survive only on fat from dusk until dawn they may have a problem. Since they likely did not have a large amount of carbohydrate available at all times they would likely be pushing all consumed carbohydrate into muscles when they are insulin sensitive and quickly reverting to fatty acid metabolism. This would be fine during the day as they could forage and hunt for food to keep energy up. During the evening however, if all they used is fat reserves they could quickly deplete their fat stores before morning and have trouble maintaining a healthy level of fat and die off. This would place adequate stress for adaptation. That adaptation could be the ability to reduce insulins effect of clearing glucose from the blood in the evening in order to have a supply in the blood to use throughout the evening to reduce the necessity of utilizing only fat as fuel and preserving the valuable reserve fuel source.
Being insulin resistant at night makes sense on several other levels as well. The brain is hungry. It uses approximately 600 calories per day. If we were completely insulin sensitive at night and just pushed all glucose into muscles and liver, the brains use of glucose would quickly deplete blood glucose resulting in hypoglycaemia. This would result in a rise in cortisol in order to stimulate the pancreas to increase glucagon in order to bring blood glucose back to a safe level. A rise in cortisol and glucagon would not result in a very peaceful sleep. The glucagon would start flooding the system with energy from stored glycogen and fatty acids alike. This would quickly wake us up and quickly deplete stored glucose and increase fatty acid metabolism which would further reduce fat stores. In todays situation that may not be a bad thing since most of us have plenty to spare but back then this would surely mean a quick death.
So back to what this means in relation to the conventional wisdom I stated at the beginning of this article.
As the study I linked to clearly shows, we are more insulin sensitive in the morning and less insulin sensitive at night. Since this is true and when we are insulin sensitive we are better able to take in and distribute nutrients, it only makes absolute sense that the best time of day to eat a large nutrient dense meal is first thing in the morning. This also means that when we are less insulin sensitive we are less able to distribute incoming nutrients. With that being true, the least beneficial time to eat is in the evening.
Breakfast is the most important meal of the day and eating too close to bed can result in weight issues. There are clear reasons why people used to have no problems with weight. Long before we had all these studies and we relied on conventional wisdom we seemed to have a more intuitive sense of how to eat. Now we seem to rely too much on results of this study or that study and it is only resulting in more confusion and poor health. On the flip side, if we start looking into why conventional wisdom may be right, we can see that the intuitive nature of our ancestors seems to be guided by ur physiology and perhaps our intuition is a much better guide than the latest nutritional study.
More studies showing breakfast is king.
Larger breakfast leads to expression of weight loss genes
Eating larger breakfast results in dramatically reduced BMI compared to skipping breakfast
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