Many would say it's the most important meal of the day.
But, lately, there has been a camp who are all-in on the benefits of intermittent fasting – skipping breakfast and waiting until lunch whether for health benefits or to avoid gastrointestinal issues during training.
So which camp is right?
Of course, what even constitutes breakfast is up for debate.
Is it just the first meal eaten, regardless of time? A.K.A. "breaking the fast"?
Or is it a meal eaten specifically in the morning?
Regardless, there are less people eating within an hour of waking, as was perhaps the case a few decades ago.
A 2009 paper shed some light on an interesting phenomenon that pertains to this question: ‘To skip or not to skip’ breakfast. They found that there’s a 70% greater rise in blood glucose after breakfast in the morning than for a similar meal at lunch time. Some research into this on the part of the authors revealed this effect, the so-called “second meal effect”, was discovered almost 100 years earlier.
WHAT IS THE SECOND MEAL EFFECT
In short, the “second meal effect” is the phenomenon where skipping breakfast results in a higher glucose spike at lunch than it would for the same meal if you had eaten breakfast. Or: Eating breakfast will ensure a lower glucose response at lunch.
That’s right: Eating carbohydrates in the morning improves your glucose tolerance at lunch.
Another interesting part of the second meal effect: The rate of glucose used for muscle glycogen synthesis after lunch is around 50% higher within 2 hours of lunch, and 100% higher within 5 hours of lunch when breakfast was eaten. That’s compared to skipping breakfast. This is a crucial factor if you are looking to prime for exercise, as this effect greatly improves your ability to store glycogen, better preparing your fuel stores for upcoming training.
WHAT CAUSES THE SECOND MEAL EFFECT
The metabolic state of the body, or the set of active metabolic and biochemical mechanisms (hormones, cellular signals, energy status, etc.), seems to be the big driver of the second meal effect.
Low insulin and high fatty acids in the blood when fasting in comparison to higher insulin and lower fatty acid levels when breakfast was eaten.
To simplify: When there is enough glucose from breakfast, glucose can and will be stored by insulin, lowering your response to eating carbohydrates at your next meal.
THE ROLE OF CARBOHYDRATES IN THE SECOND MEAL EFFECT
Aside from eating carbohydrates, the type of carbohydrates, specifically low glycemic index rather than high GI seems to further lower the glucose response to the second meal. Similarly, fermentable carbohydrates also seem to lower the impact of the second meal effect.
High protein breakfasts actually look to attenuate the second meal effect too. (Though, in these studies, the meals eaten were still relatively high in carbohydrate – 35% protein, 45% carbohydrate – at times, so this is still not very clear.)
WHAT THIS MEANS
- The second meal effect can help drive glycogen storage more effectively when you are preparing for training and racing. Ensuring you are eating carbohydrates regularly (starting with breakfast) will help ensure your glycogen stores are full.
- It can help blunt glucose spikes at lunch and limit glucose variability.
THE MISSING PIECES
There is still a lot to be learned about the second meal effect. Specifically related to dosing of macronutrients and individual variation. It is still uncertain exactly how much carbohydrate is needed to prevent the second meal effect and if this differs between individuals.
Fortunately, individuals' responses can better inform action and adjustments while the nuances are teased out by the scientific community. In addition, having visibility on an individual’s personal response will definitely be more relevant than a group based inference when custom changes need to be applied.
For those individuals specifically wanting to know more about their own response versus that of the group in the specific research study, real time visibility will allow you to iterate your own dosing and work out your individual response. You can use the second meal effect to your advantage… or at least with intention.
- Jovanovic, A., Leverton, E., Solanky, B., Ravikumar, B., Snaar, J. E. M., Morris, P. G., & Taylor, R. (2009). The second-meal phenomenon is associated with enhanced muscle glycogen storage in humans. Clinical Science, 117(3), 119–127. doi:10.1042/cs20080542
- Jovanovic A, Gerrard J, Taylor R. The second-meal phenomenon in type 2 diabetes. Diabetes Care. 2009;32(7):1199-1201. doi:10.2337/dc08-2196
- Staub H. Examination of sugar metabolisms in humans. Z Klin Med 1921;91:44–8.
- Traugott K. In reference to the reactions of blood sugar levels in repeated and varied types of enteral sugar increases and their significance in liver function. Klin Wochenschr 1922;1:892–4.
- Takafumi Ando, Satoshi Nakae, Chiyoko Usui, Eiichi Yoshimura, Nobuo Nishi, Hidemi Takimoto, Shigeho Tanaka, Effect of diurnal variations in the carbohydrate and fat composition of meals on postprandial glycemic response in healthy adults: a novel insight for the second-meal phenomenon, The American Journal of Clinical Nutrition, Volume 108, Issue 2, August 2018, Pages 332–342, https://doi.org/10.1093/ajcn/nqy086
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- Brighenti F, Benini L, Del Rio D, Casiraghi C, Pellegrini N, Scazzina F, Jenkins DJ, Vantini I. Colonic fermentation of indigestible carbohydrates contributes to the second-meal effect. Am J Clin Nutr. 2006 Apr;83(4):817-22. doi: 10.1093/ajcn/83.4.817. PMID: 16600933.
- Park YM, Heden TD, Liu Y, Nyhoff LM, Thyfault JP, Leidy HJ, Kanaley JA. A high-protein breakfast induces greater insulin and glucose-dependent insulinotropic peptide responses to a subsequent lunch meal in individuals with type 2 diabetes. J Nutr. 2015 Mar;145(3):452-8. doi: 10.3945/jn.114.202549. Epub 2014 Dec 24. PMID: 25733459; PMCID: PMC6619673.
- Meng H, Matthan NR, Ausman LM, Lichtenstein AH. Effect of prior meal macronutrient composition on postprandial glycemic responses and glycemic index and glycemic load value determinations. Am J Clin Nutr. 2017;106(5):1246-1256. doi:10.3945/ajcn.117.162727