We have all heard the old adage that “Breakfast is the most important meal of the day,” but can such an adage be proven scientifically? And if so, by what criteria do we measure the importance of one meal over another, and perhaps most importantly, would this be true for everyone?


In the dietary principles we lay out in chapter 8 of The Original Prescription, principle #3 reads: “Unless purposely fasting, don’t skip meals. Start each day with a balanced breakfast containing both protein and fiber.” I mention, among other things, that the glycemic dynamics after the morning meal have a powerful impact on hunger signals throughout the day. I also mention how the diurnal rhythm of the stress hormone cortisol, which peaks in the morning just after awakening, is supposed to steadily drop during the time one normally consumes breakfast. Of course, cortisol is one the body’s modulators of glucose and insulin action and, I believe, one of the reasons that stress, insulin sensitivity, eating breakfast and risk for obesity and metabolic disorders are related. Skipping breakfast, as most of you know, is linked with increased risk for obesity, insulin resistance, diabetes and heart disease. Among other things, the need for our bodies to maintain higher cortisol to sustain our glucose levels when we skip our breakfast meals (remember cortisol is a gluco-corticoid), diminishes our insulin sensitivity and increases the overall catabolic effect of cortisol- driving more metabolic dysfunction.

As we discuss in the book in detail, our bodies are designed to take in the “signals” of our life(style) and convert this into health. As with many of the signals that follow a circadian rhythm like cortisol, researchers have now identified that insulin secretion and action follows a pattern based on a diurnal pattern of pancreatic beta cell function. And would you believe, glucose tolerance and insulin sensitivity is highest after breakfast. Researchers at the Mayo Clinic measured a number of parameters of beta-cell function and insulin and glucose metabolism and discovered that total beta cell responsiveness was over 20% higher after breakfast than after either lunch or dinner [Pub Med Link]. Overall, this pattern was maintained amongst most of the participants, but it was not so in every person measured (they studied “healthy” normal weight volunteers with normal fasting glucose). They found, that in a few individuals, morning insulin sensitivity and beta cell function was dramatically lower after breakfast than after lunch or dinner. What is going on in these individuals?

The authors speculate that individual responses may be influenced by sleep-wake cycles, age, gender, shift work or jet lag. Of course, my first question was “What are the cortisol levels in these individuals?” The author emailed me that cortisol, among other hormones, was monitored in these individuals and the data is being studied for a future publication (we will have to wait). I think this information will help us understand why some individuals responded differently to the group as a whole. I can tell you, as someone who attempted a similar study; that performing a glucose/insulin test after breakfast without controlling for wake time and shift work will dramatically influence the individual responses.

How I read this data with what we know already:

  • Insulin sensitivity follows a diurnal rhythm- corresponding with the normal sharp drop in cortisol in the AM (the hypothalamus is controlling all of this).
  • After an 8-12 hour fast, the body appears to be designed to dispose of a larger meal by increasing beta-cell function and peripheral insulin action.
  • Eating breakfast helps to ensure the normal drop off in cortisol levels after awakening.
  • Skipping breakfast means we miss the window when our body is designed to most efficiently deal with a meal and, among other things, triggers cortisol production and a subsequent increased desire for comfort foods.
  • This pre-programmed increase in insulin and beta cell action after breakfast can be eliminated by improperly timing the first meal of the day due to awakening time (shift work, jet lag, poor sleep) or HPA axis stress.
  • The link between elevated stress, skipping breakfast and a wide-range of metabolic disorders is not a coincidence.

In my next post, I will discuss how exercising before breakfast might affect your metabolism.
Here are few more related articles to ponder:

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