Should You Restrict CHO Pre-Workout For Fat Loss?

+ A decision tree

There are a couple takeaways concering the consumption and timing of CHO in relation to maximizing fat oxidation (Source: Optimizing fat oxidation through exercise and diet — PubMed (nih.gov)):

1. Acute ingestion (and type) of CHO immediately before exercise reduces fat oxidation.
2. The effect of CHO ingestion during exercise on fat oxidation depends on exercise intensity. During low- and moderate-intensity exercise, CHO intake reduces fat oxidation similarly to when CHO is ingested before exercise. However, during high-intensity exercise, studies show no significant difference in fat oxidation between fasted and fed states.
3. Chronic dietary changes, such as high-fat diets, have been shown to influence fat oxidation. High-fat, low-CHO diets can lead to increased fat oxidation. The specific timeframe for observing this increase can vary but is generally within several days to a few weeks.

The question, then, however becomes “Should you do this in the first place?” Hence I made the following decision tree:

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Background

Are you trying to lose fat?

1. If you aren’t trying to lose fat, it might be better to consume carbohydrates pre-, intra-, and post-workout to enhance the training session itself (physiologically, if the duration is long enough, but also mentally e.g. more feeling of energy although the latter could perhaps also be done via high protein/fat foods), but also recovery and enhance next-session performance.
2. If you are trying to lose fat coupled with low- to moderation-intensity training, CHO restriction pre- and intra-workout might be more beneficial due to glycogen sparing via increased fat oxidation (see research cited above).
3. Point number 2, however, does require the end result to be different (or it would make little sense whether you chose to restrict CHO pre-/intra-workout or not) i.e. you need to use this glycogen sparing in combination with a higher total deficit that specific training day.
4. Essentially, we are trying to make use of this glycogen sparing in order to minimize any possible reductions in next-session performances.

Do you have a hard time eating very little food?

1. If you already have a hard time eating very little food (e.g. hunger or simply having a hard time fitting all the food within a specific time frame), eating even less food (especially the longer you are in a hypocaloric diet) could make the diet unsustainable.
2. However, point number 1 could still, perhaps, be done by eating just a bit more food but not so much that it nullifies the calories burned through exercise e.g. if you burn 500 calories through exercise and only eat 400 of those calories back, then that’s still -100 calories added on top of the deficit you already had chosen that day.
3. If you don’t have a hard time eating very little (e.g. you are still in the early phase of your hypocaloric diet or you simply don’t crave a lot of food), then creating a larger deficit through exercise might be better than doing the same thing without exercise (e.g. because you can meet your macro- and micronutrient needs more easily). Besides, there are many more benefits such as maintaining/increasing fitness or enhanced recovery when exercising in Zone 1.

As expected, VO2peak was significantly improved after 6 months of intervention in CR+EX only (22±5% vs. 7±5% in CR and −5±3% in CO) whereas isokinetic muscular strength did not change. There was no difference in the losses of weight, fat mass or visceral fat and changes in systolic BP between the intervention groups. However, only CR+EX had a significant decrease in diastolic BP (−5±3% vs. −2±2% in CR and −1±2% in CO), in LDL-cholesterol (−13±4% vs. −6±3% in CR and 2±4% in CO), and a significant increase in insulin sensitivity (66±22% vs. 40±20% in CR and 1±11% in CO).

>CR = caloric restriction
>EX = aerobic exercise

Source: Caloric Restriction with or without Exercise: The Fitness vs. Fatness Debate — PMC (nih.gov)

Do you want to be in an even bigger caloric deficit?

1. If not, then the possible benefits of consuming carbohydrates pre-/intra-workout (e.g. more mental energy, enhanced recovery) might outweigh the benefits of not doing so. A possible argument could be made that when exercising in Zone 1 (or even lower Zone 2), when done with short durations, are light enough that it shouldn’t really hinder intra- and next-session performance too much, but a counterargument to this could also be made like the aforementioned (e.g. enhanced recovery).
2. If yes, then you could try to create an even larger caloric deficit by partially feeding yourself to none at all depending on the calories burned through exercise.

Is it hampering your next-session performance too much?

1. If not, continue doing carbohydrate restriction pre-/intra-workout (and perhaps try to increase the total daily deficit even more if it still doesn’t hinder next-session performance as well as having no trouble with the other points mentioned).
2. If yes, then you have to make a decision whether losing fat is worth the sacrifice in possible fitness gains (and perhaps even losses). Short-term fitness losses could perhaps not be much of a problem, although stretching this out too far into the future could lead to overtraining:

Overtraining syndrome (OTS) occurred independently from excessive training, since insufficient calorie, protein, or carbohydrate intake, poor sleep quality, or concurrent excessive cognitive effort were the found to be prevailing predictors of OTS.

…we identified the following risk factors or predictors of OTS23 : (i) mean number of daily hours of work/study >8 hours/day; (ii) carbohydrate intake <5.0 g/kg/day; (iii) protein intake <1.6 g/kg/day and (iv) total daily calorie intake <35 kcal/kg/day.23 Fat intake (g/kg/day) did not predict OTS.23 This reinforces the theory that OTS rises from unique combinations of risk factors and stressors, rather than excessive training alone.

Source: Novel insights of overtraining syndrome discovered from the EROS study — PMC (nih.gov)

Timing of Endurance Exercise To Maximize Fat Oxidation

According to the following study, exercising in the afternoon increases maximal fat oxidation more than in the morning, which is further increased through caffeine:

Time-of-day also had a significant effect on Fatmax (all P < 0.01), which was always higher (ranging from 11.1 to 13.1%) in the afternoon than in the morning. Compared to the placebo, caffeine intake increased Fatmax by 11.1% in the morning (36.9 ± 14.4 vs. 41.0 ± 13.1% respectively; d = 0.30; Fig. 3) and by 13.1% in the afternoon (42.0 ± 11.6 vs. 47.5 ± 10.8%, respectively; d = 0.49; ​Fig.3)

Source: Caffeine increases maximal fat oxidation during a graded exercise test: is there a diurnal variation? — PMC (nih.gov)

Extra: Studies have shown that the combination of Ephedrine and Caffeine is superior for fat loss than taking each individually.[1][2][3] As ephedrine can increase heart rate and caffeine may increase blood pressure (in a naive user), the combination tends to have an additive rather than synergistic toxicological profile.[4]

The aspirin is added to prevent blood clotting (which may be a side effect of ephedrine) and to aid in the signal transduction of ephedrine via prostaglandin inhibition.

Source: ECA benefits, dosage, and side effects (examine.com)

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