Prof. Dr. Andro « Paleo Diet – Paleolithic Diet Research, Primal Nutrition, Low-carb eating, Eat like a caveman
As the data in
figure 2 tells you, there is
no difference in the following hours and – what’s even more important – the total energy expenditure was identical – 2594kcal/day vs. 2589kcal/day in the before and after breakfast trial, respectively. In addition to that, a detailed analysis of the unpublished study by Shimada et al. the above data was taken from, does also show that
- working out before breakfast reduces the energy expenditure in the time before lunch – over the whole period the subjects burned about 500 kcal less, when exercise was performed before breakfast
- working out before breakfast burns more glycogen and increases non-oxidative carbohydrate storage during / after breakfast — with the carbohydrate content of the breakfast being used for glycogen repletion, this does in fact lead to another increase in fatty acid oxidation, simply because the alternative fuel, namely the carbs are not oxidized, but stored
So, 2x thumbs up for cardio
before breakfast – at least in the short run and when your goal is to maximize fatty acid oxidation, but …
Is maximal fatty acid oxidation even what you should be aiming for during a workout?
I guess you will already have read between the previous lines that my answer to this question is a definitive “no”. Moreover, most of you are so clever and have been following the
SuppVersity posts for so long that they could come up with their own arguments against an overemphasis of intra-, post and total 24h fatty acid oxidation, when getting lean and healthy is your goal. And probably, some of them are even identical to mine:
- Firstly, and most importantly, burning fatty acids for fuel does not equate fat loss. If you follow a real ketogenic diet (not one with tons of protein in it), you’ll burn (almost) exclusively fat, but even under these “extreme” conditions most of the fat will come from the fat you eat, while the small amount that’s actually taken from your hips, buttocks and whatever, will be restored unless you are in a caloric deficit, when your fatty acid oxidation will increase anyways.
- Secondly, many of the metabolic benefits of exercise are closely related to the act of glycogen depletion. This is particularly true for the increase in GLUT-4 expression and consequent improvements in muscular glucose uptake, burning only fat for fuel during a workout is thus a questionable ideal.
- Thirdly, working out “in the zone” may burn the most fat but won’t have the conditioning effects high(er) intensity workouts have. While obese individuals and people who have been sitting around their whole lives will see improvements in their VO2max (and in the long run their heart-health), anyone who is not totally unconditioned misses out on the structural changes in the musculature, and as you’ve learned on day one of the SuppVersity Exercise Science Week adipose tissue, as well.
In short, the importance of burning fat for fuel is so overrated that exercise prescriptions that are based on the paradigm of maximal fatty acid oxidation are at least suboptimal for health, fitness and physique purposes.
Some people, I guess, would probably even go so far to say that they do more harm than good. I for my part leave it up do you to decide whether you join sides with my carefully worded or the more extreme version of this conclusion, or – and this would be your good right – to wholeheartedly disagree with both of them.
References:
- Ballor DL, RE Keesey. A meta-analysis of the factors affecting exercise-induced changes in body mass, fat mass and fat-free mass in males and females. Int J Obes. 191; 15: 717-726.
- Bielinski R, Schutz Y, Jéquier E. Energy metabolism during the postexercise recovery in man. Am J Clin Nutr. 1985;42: 69-82.
- Dionne I, Van Vugt S, Tremblay A. Postexercise macro-nutrient oxidation : a factor dependent on postexercise mac-ronutrient intake. Am J Clin Nutr69: 927-930.
- Donnelly JE, Smith BK. Is exercise effective for weight loss with ad libitum diet? Energy balance, compensation and gender differences. Exerc Sport Sci Rev. 2005; 33: 169-174.
- Henderson GC, Fattor JA, Horninig MA, Faghihnia N, Johnson ML, Mau TL, Luke-Zeitoun M, Brooks GA. Lipolysis and fatty acid metabolism in men and women during the postexercise recovery period. J Physiol. 2007; 584: 963-981
- Hill JO. 1992. Physical activity and energy expenditure pro-ceedings: national task force on prevention and treatment of obesity. Physical activity and obesity conference – NIDDK, pp.60-65.
- Iwayama K, Tokuyama K. Exercise in a metabolic chamber – Effects of exercise on 24 h fat oxidation. J Phys Fitness Sports Med. 2012; 1(2): 307-316.
- Melanson EL, Sharp TE, Seagle HM, Horton TJ, Do-nahoo WT, Grunwald GK, Hamilton JT, Hill JP. Effect of exercise intensity on 24-h energy expenditure and nutrient oxidation. J Appl Physiol. 2002; 92: 1045-1052
- Shimada K, Yamamoto Y, Iwayama K, Nakamura K, Ya-maguchi S, Hibi M, Nabekura Y, Tokuyama T (unpublished observation).
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