I’ve posted before about nutrient timing suggestions to maximize your health and performance.  But since some folks want to know the why, or are just plain skeptical, I wanted to write up an article that outlines some of the research behind optimal timing of your macronutrients.

Perhaps the most misunderstood aspect of nutrient timing is breakfast.  It’s been traditional wisdom to have carbs for breakfast. but as you’ll see, there’s pretty clear evidence to the contrary.

I’m sure part of the disconnect stems from our obsession with “breakfast food” – pancakes, waffles, toast, muffins, bagels, and cereal.  And even if the health-conscious eater avoids these gluten-rich foods, he may make the presumably better choice of oatmeal and fruit.  Another cause of high carb breakfasts might come from the well-accepted idea that you will burn off the carbs later in the day.  Unfortunately, it doesn’t quite work that way.

To optimize your body composition, you need to consider the body’s two primary fuel sources – fat and carbohydrates.  The goal should be to use the right fuel at the right time.  This ability to shift between fuel sources is known as METABOLIC FLEXIBILITY.

We won’t use both fat and carbs simultaneously.  When performing glycogen-demanding exercise (like Crossfit or Brazilian Jiu Jitsu), we need access to those stored carbs.  But during endurance work or any other non-training times of the day, we should be able to use fat as fuel.  This is metabolic flexibility.

Those people that are metabolically inflexible are prone to diseases like diabetes and obesity.  They do not use fat and carbs at the right time, and end up storing them.  In the morning, the time that they should be using fat, they’re not.  So they will be using glycogen or they will break down protein to convert to carbs.  Either way it causes a greater demand for carbs, which they already don’t manage well.

So how does this relate to breakfast?

After an overnight fast (i.e., sleeping), insulin levels are low and muscle glycogen is full, which means we are in an ideal state to use fat as fuel.  Eating fat will promote that signaling, whereas eating carbs spikes insulin and tells your body to start using carbs as fuel.

* Side note: If you’ve heard that glycogen stores are depleted after an overnight fast,  it’s your LIVER glycogen stores that are depleted, not muscle (unless you exercised in your sleep).

Granted, you do wake up in the morning very insulin sensitive.  But that means your fat cells are also insulin sensitive.  And again, unless you sleep-exercised, there has been no stimulus to preferentially shuttle those carbs to the muscle cells.

Of course, there are other factors determining your ability to use fat as fuel.  Such as genetics and training.  But even if you’re prone to be inflexible, you can change it with diet.

The final idea I want to leave you with is perhaps the most convincing element of the protein & fat breakfast recommendation.


Nutrient programming is the idea that what you eat for breakfast programs how you handle nutrients throughout the rest of the day.  Well, it’s more than just an idea.  It’s been proven.

Dr. Molly Bray, at the University of Alabama at Birmingham, published a study in the International Journal of Obesity revealing that breakfast dictates your preferred fuel source for the rest of the day.(1)

She took two groups, and had them eat the exact same daily amount of carbs, fat, and protein.  Total calories were identical.  Macro breakdowns were identical.  Food types were identical.

One group had a higher carb breakfast and split the remainder of the carbs throughout the day.  The other group had a zero-carb breakfast and ate their carbs later throughout the day.

The group that ate protein and fat for breakfast became more insulin sensitive and leaner.  Conclusion:  “The time of day at which carbohydrate versus fat is consumed markedly influences multiple cardiometabolic syndrome parameters.”(1)

Hopefully this sheds some light on the ramifications of including carbohydrates in your first meal.  Whether you are trying to optimized body composition, health, or performance, all the science points towards a high fat and protein breakfast.

Oh, and as a side note, studies show that people who skip breakfast are more prone to store fat.


1.  Bray et al. Time-of-day-dependent dietary fat consumption influences multiple cardiometabolic syndrome parameters in mice. International Journal of Obesity, 2010; DOI: 10.1038/ijo.2010.63


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