Don’t Eat Carbs for Breakfast!

Probably one of the most common dietary advices is: „Start your day with healthy carbs, like oatmeal, because that will give You energy!” The second most common is: „Eat no carbs in the evening because your body will not be able to burn it and you will convert it to fat!” (Seriously: WTF?!) These reflex-like dogmas are engraved in our brain. But what does science have to say about them? What’s the truth?


In the following article I will confuse the assumptions, beliefs and dogmas with facts.

(For the facts and summary – click here!)

First of all, let’s take a look at why we consume carbs! The human body is capable of producing energy from – in order of the body’s preference – fats, carbs and proteins. The primary fuels are fats and carbs. The ratio of energy from fats vs. energy from carbs is defined by the respiratory quotient, also known as the RQ. The value of the RQ ranges between 0,7 and 1, where 0,7 marks 100 % fat burning, while 1 marks 100 % carb burning. (This value measures the amount of inspired O2 compared to the exhaled CO2, and is based on the fact that it takes more oxigen to burn 1 molecule of fat than to burn 1 molecule of glucose.)

The presence of fat deposits is quiet obvious (actually, we are constantly trying to get rid of them). Our carb deposits, called glycogen, are in the skeletal muscles and the liver. The role of muscle glycogen is to produce energy (ATP), while liver glycogen is responsible for maintaining blood glucose levels between meals. Blood glucose must be maintained as there are some cells – red blood cells, neurons, cells of the renal medulla – that are unable to use fat for fuel. (Neurons can burn fat, but free fatty acids can’t cross the blood-brain barrier.) Maintaining blood glucose is crucial: you can live 10-20 years with elevated blood glucose, but no more than 5 minutes with a severe hypoglycaemia! That is why there are many hormones that can raise blood glucose (glucagon, cortisol, adrenaline, growth hormone), but only one can decrease it (insulin). (Our central nervous system can supply up to 80 % of its energy needs from ketones.)

Now let’s look at what happens when fasting! Assume, that we just ate, all our „warehouses” are full. Our insulin starts to decrease and slowly reaches baseline blood levels. All the food we ate has been stored, our blood glucose is 90 mg/dl (5 mmol/l). What happens next? As our cells live and function, perform their duties they consume energy. After a carb rich meal most of that energy is from glucose – that is, our body starts to use up its blood glucose. As blood glucose starts to drop, the body starts to reprogram the way it operates: maintaining a steady blood glucose level is of outmost importance! Every cell that could use, should use fatty acids for fuel (thus decreasing the number of blood glucose using cells). Processes aiding fat burning and blood glucose maintenance start – there’s an increase in hormones like glucagon, cortisol, growth hormone. The liver starts to break down its glycogen stores and pumps glucose into the blood. All the while all tissues capable of using fat for fuel start burning fatty acids via β-oxidation. The amount of liver glycogen is sufficient for upholding blood glucose for about 24 hours. After that the liver starts to synthesize glucose from alternative materials (glycerol, lactate, amino acids). Now I can hear You freaking out: „I’m burning my muscles!” Calm down, in the first 24 hours there’s practically no muscle loss – the resynthesis of glucose is still at a low level, and the glycerol from lipolysis supplies sufficient amount of starting material. (Note: that means, if you had dinner last night, you will not lose muscle while you’re asleep, not even if you skip breakfast!)

The process I just outlined happens to all of us. Every single night. You go to bed, normoglycemia and normal insulin levels are restored in 2 hours after a meal. Glucagon levels start to rise with growth hormone and lipolysis is increasing. When we wake up the next morning we are in full-blown fat burning mode – most tissues in our body have adopted fat burning as their primary source of energy, and we’re about to become a fat burning machine. But OH, NO! What do we do first thing in the morning? That’s right, You guessed it: we eat our oatmeal-whey protein breakfast. The result? Insulin through the roof, fat burning through the floor. Everything is back to burning what we just ate – that is: carbs.

Let’s take a look at the hormones controlling our blood sugar:

  • Adrenaline and noradrenaline is secreted by the adrenals during times of stress or in emergency. In times like these, our body is trying to increase the energy available and accessible to the muscles and the brain, thus making survival more likely. Both hormones have diurnal daily rythms meaning they have a max. and a min. concentration throughout the day. The max. for noradrenaline is at 2-3 o’clock AM, with adrenaline following one hour behind.
  • Cortisol, called the „stress hormone”. It’s secreted by the adrenals into the blood in times of stress. It has a daily, also known as circadian rythm with a maximum concentration in the morning (thus we wake up), and slowly decreasing throughout the day to its night time minimum (when we fall asleep). Cortisol decreases insulin sensitivity in the peripheral tissues (e.g. skeletal muscles) – this is a way of conserving blood glucose.
  • Growth hormone has metabolic effects in addition to the role it play in growth and development. In times of fasting, growth hormone raises blood glucose and decreases insulin sensitivity in peripheral tissues. It has a pulsatile secretory pattern with a daily maximum concentration around 2 AM and a minimum at 3 PM.

So, in the morning we have high cortisol, a decreasing but still high growth hormone. Our blood sugar is under control (in the 65-99 mg/dl or 3,5-5,5 mmol/l range)! How do we know? We are still alive. The peripheral tissues (muscles) have poor insulin sensitivity. We are in fat burning mode and our muscles are intact. (Remember? Liver glycogen keeps blood sugar stable for 24 hours without much glucose resynthesis.) So we are burning fat and conserving muscle. But our insulin sensitivity is poor!

Consuming carbs at this inappropiate time causes numerous problems:

  • It disrupts our circadian rythm by decreasing cortisol when it should be high.
  • Thanks to poor insulin sensitivity, our blood sugar goes through the roof.
  • The carbs consumed are converted to fat.

What we eat in the morning will determine our respiratory quotient (RQ) for the whole day. In other words: our breakfast determines what source of energy (carbs or fats) our body will prefer throughout the whole day! Studies have shown, that a high-fat breakfast followed by high carb meals leads to higher lipolysis, lower RQ, improved glucose tolerance, and lower overall calorie intake compared to a high-carb breakfast followed by high fat meals.[1]

Now when we eat carbs, insulin levels rise. Insulin decreases the amount of big neutral amino acids in the blood except the amount of tryptophan. This will increase the tryptophan:other amino acids ratio, resulting in an increase of the brain’s tryptophan uptake. Tryptophan is the starting material of one of the most important neurotransmitter of our brain: serotonin. The effect is dependent on the carb-to-protein ratio of the meal – as tryptophan is the least abundant amino acid in our food, eating protein raises blood levels of most big neutral amino acids, except that of tryptophan and so the tryptophan-amino acid ratio can remain unchanged.[2-8] Serotonin has a major calming effect on our central nervous system. Though this may sound good, but in reality we end up with zero concentration and – hands up if this happens to you – tend to fall asleep right after breakfast. Furthermore, our morning meal determines our food preference and uptake for the day.[8]

Okay, that does not sound that good. We got it – we won’t eat carbs and oatmeal with whey for breakfast. But what should we eat? Well, protein and fat! If we want to be able to concentrate we need starting material of neurotransmitters dopamine and acetyl-choline – we need to eat protein (supplies amino acid tyrosine, important in dopamine sythesis) and choline found in fatty foods (for the synthesis of acetyl-choline). My personal favourite is bacon and eggs, with grass-fed butter and some sour cream.

I hear You: „Good, but when can I have my carbs?” Let’s go back to the daily hormonal rythm: our insulin sensitivity is at the top during mid day (12 AM – 2 PM), and starts to decline again after that. In the evening – though it’s worse than at 12 AM, insulin sensitivity is still higher than in the morning.[12]

Consuming most of your carbs at night has other benefits as well: at night, when we fall asleep melatonin („the sleep hormone”) levels rise – mostly due to darkness. The rise in melatonin increases growth hormone, which aids fat burning and recovery. If you eat carbs in the evening, serotonin concentration in the brain will increase. Serotonin calms the brain and helps the secretion of melatonin. Higher melatonin results in a decrease in catabolic hormones’ consumption of our muscle proteins. At this time of the day, carbs aid our circadian rythm. Many scientific studies show that circadian rythm is probably one of the most important factors in obtaining healthy glucose control.[13]

Scientific studies verify these statements – subjects were divided into 2 groups. Participants in group 1 consumed carbs throughout the day, group 2 ate nearly all carbs in the evening. The results were the following:

The group eating carbs all day lost more weight (3,9 kg vs. 3,3 kg), BUT out of those 3,9 kg 1,3 was fat free mass (mostly muscle). In the evening carb group out of that 3,3 kg only 0,3 kg was fat free mass. So the all day group lost 2,6 kg of fat, while the evening group lost 3 kg.[11]

Studies comparing the effect of morning or evening carb consumption found the following:

People consuming carbs in the evening had:

  • decreased average insulin levels, fasted blood glucose and increased insulin sensitivity throughout the day,
  • decreased LDL-cholesterol and triglyceride, and increased HDL-cholesterol levels,
  • decreased inflammatory markers (CRP, TNFα, IL6).[9]
  • decreased leptin levels (hormone singaling „I’m full!”), the daily concentration curve changed – minimum is reached only at the evening (you feel full during the day),
  • decrease in the levels of the hunger hormone ghrelin, the daily concentration curve changed instead of a mid day max. it had a minimum value in the afternoon and rose to a max in the evening (thus you are not hungry during the day),
  • increased adiponectin levels (aids lipolysis).

Summary: if you save your carbs for later in the day both your physique and your health will improve. Forget oatmeal with whey for breakfast and the „all-day-carbs”. Eat breakfast when you feel hungry, and eat protein and fat for breakfast. Eat carbs for dinner.


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