Last week I introduced an article which looked at the effect of fasting on exercise and metabolism. Because I am a healthy weight individual with an active exercise regimen, the research surrounding IF and exercise is highly interesting to me. This week, we’ll take a look at some recent research published in The American Journal of Physiology, “Preexercise breakfast ingestion versus extended overnight fasting increases postprandial glucose flux after exercise in healthy men”.
The aim of this study was to assess how a fed versus fasted state impacted after-exercise glucose metabolism rates (following a dose of glucose given almost immediately after the workout), and also looked at the utilization of carbohydrates versus muscle glycogen (stored glucose/carbs) versus fat for fuel during exercise in the fed versus fasted athletes.
Our bodies will use glucose for energy during exercise when glucose is readily available in our blood. When glucose starts to run low, the body will solicit glucose by tapping into glycogen reserves in the muscle, and also use some fat for fuel (which turns into ketones, not glucose).
In this study:
- 12 men – average age 23 years, average BMI 23.6 (healthy), average body fat 14%
- Split into three groups:
- BR = Breakfast – Rested (no exercise)
- BE = Breakfast – Exercise (fed, then exercised)
- FE = Fasted – Exercise (12-14 hour overnight fast before exercise)
- BR and BE groups were give a porridge made with oats and milk which provided 430 calories, 65g carbs and 19g protein. BR then rested for three hours, BE rested for two hours before initiating 60min of cycling
- FE did not get calories before the 60min of cycling
- BE and FE were given a 75g oral glucose tolerance test immediately after the workout
- Peak glucose levels: NO DIFFERENCE between BE/FE
- BE group saw increased rate of glucose metabolism during the oral glucose tolerance test
- 73g glucose used during 120min versus 44g glucose used during same time in FE group
- Blood insulin levels: lower in BE group than FE group
- Macronutrient utlization:
- BE group used more blood glucose and glycogen
- FE group used more fat
The authors performed this research to prove a point that “metabolic responses to fed state exercise cannot be readily inferred from studies in the fasted state.” Many studies looking at glucose utilization require participants to be fasted before the study begins, when in reality most people exercise after having a meal. Thus, the authors accurately reveal that the results of a fasted-participant study cannot be translated directly to fed-state real life people.
One of the most interesting highlights of this study, to me, was that “at rest, breakfast consumption improves glucose tolerance and insulin sensitivity at subsequent meals [known as the “second-meal effect”].” It seems counter intuitive that eating a meal would result in less insulin the blood but similar glucose uptake the next time a meal is eaten. Both exercise and carbohydrate presence cause the release insulin, which helps muscles take up glucose. So it would seem that maybe the absence of the first carbohydrate meal blunted the insulin effect which was seen in the BE group.
The authors continue: Our findings show that breakfast ingestion (vs. fasting) before exercise enhances subsequent glucose disposal at postexercise meals in the presence of lower insulinemia, suggesting that the second-meal effect is maintained even if exercise is performed between meals.”
The human body is truly an awe-inspiring machine. Of course this was a small sample size of young men and the research conducted over a short period of time, but this was an exciting article to read (<< NERD). The finding that the fasted state participants used more fat for fuel and less glucose AND glycogen is a plus for IF in my eyes. The minus – that insulin levels were higher and glucose metabolism slower in the fasted participants after their post-workout meal. However, this meal was concentrated glucose, not a meal composed of protein, glucose and fat which together will slow the rate that glucose hits the bloodstream… anyhow, onto the next stuff.
First week of the month means… Measurements Update!
Not a lot of words for these results. I feel great, healthy and have a lot of energy. I’m going to be drinking a lot of water and tea and finding ways to stay positive when I’m hangry during alternate day fasting 😛
Week 8 In Review:
This week went really well and I didn’t eat any calories after 9pm during the week or 10pm on the weekends! The challenges were nil because I planned better and I’ve gotten used to not eating until 1-2pm. The successes were great! Wednesday I missed my workout because I was caught up talking to a lawyer about a girl who’s skipped out on her rent, so I made up for that by going to crossfit on Friday (which I sometimes skip because I have two spin classes that day). All meals were from home except Saturday dinner, when I joined friends for a birthday celebration and had delicious Cuban food at Cuban Corner in Rockville, MD.
Week 9: Last week of 16:8
I’m sad that this is the last week of time restricted eating and am not looking forward to alternate day fasting. I’ll have my usual lunch except Tuesday when I meet a friend for lunch at Sweetgreen. Dinners will be left over soup. Not much planned for this weekend so I expect it to be like last weekend: dinner at home on Friday and possibly out on Saturday, when I’m hoping to head to City Winery to see the Tom Petty cover band “Damn the Torpedos”.
Hungry Harvest brought a bunch of staples and I was craving soup, so I made white bean soup with kale and chicken sausage. I found this recipe at Whole Foods years ago. It’s so fast to make and only calls for five ingredients! I meant to take pics of my prep set up then the final product but I forgot in my hungry haze. Here’s a photo of the soup from the Whole Foods website: