Carb Up to Burn More Fat!? True or False: High CHO Diet Allows for 64% Greater Intra-, Post- & Total Fat Oxidation

You could use this exercise to deplete your glycogen levels before "cardio".

The title alone will be considered an atrocity by Taubes' evangelists: "High-CHO diet increases post-exercise oxygen consumption after a supramaximal exercise bout" (Ferreira. 2016 | title of the paper in the Brazilian Journal of Medical and Biological Research). I mean, more carbs = lower fat oxidation, that's what they've been told for years. And in fact, the title says "after a supramaximal exercise bout" and thus appears to leave enough room for the low-carb run to still burn significantly more total fat. Unfortunately (for Taubes and co.), though, that's not the case.
If you take a look at the data in Figure 1, you will notice that the rate of fatty acid oxidation was significantly higher both during (EXERCISE) and after the workout (EPOC).

Figure 1: VO2 as a marker of fatty acid oxidation during (EXERCISE) and after (EPOC = excess post-exercise oxygen consumption) in 5 physically active males in response to submaximal exercise on high- vs. low-CHO diets (Ferreira. 2016).

Accordingly, the total amount of fat the subjects burned was larger, not smaller; and the effect size of ES = 1.8 further somehow reminds me of a sentence that I haven't heard ever since the rise of low-carb dieting: 'Fat burns in the fire of carbohydrates'.
Before we get deeper into the discussion of the implications of the results, however, it is imperative to take a look at the methodology of the experiment the scientists from Vitória de Santo Antão, the Universidade de São Paulo, and the Universidade Federal de Lavras have conducted last year.

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"[A]fter receiving verbal and written explanations, and signing an informed consent, 5 physically active males (age 31.0±7.7 years, height 180.2±4.3 cm, body mass 77.0±7.7 kg, body fat 13.3±2.9%, V̇O2 peak 48.6±11.5 mL·kg-1·min-1) volunteered to participate in this study [...]

In order to produce a large difference in CHO availability, pre-SE endogenous CHO stores were altered by a combination of exercise and diet" (Ferreira. 2016)

Now these "alterations" comprised (a) a glycogen-depletion exercise protocol 48 h before each experimental session. As Ferreira et al. point out, "[t]his protocol consisted of a 90-min cycling at 50% of the difference between LT1 and LT2, followed by 6×1 min exercise bouts at 125% of V̇O2 peak; 1 min recovery was allowed between effort sets" (Ferreira. 2016), and (b) different baseline diets (see light-blue box for more information about the diet - will be updated, if possible).

Figure 2: Experimental design. After the preliminary and familiarization test, and a 7-day period, participants were submitted to a glycogen-depletion exercise protocol (GDEP), followed by 48 h having either a high- or low- carbohydrate (CHO) diet. At the end of the 48-h period, participants returned to the laboratory and performed the test experiment for data collection. After a washout period of 7 days, the process was repeated with participants who had the high CHO diet previously, receiving the low CHO diet, and vice-versa (Ferrera. 2016).

After the standardized glycogen-depletion exercimse protocol, participants followed the sequentially prescribed high- or low- carbohydrate (CHO) diet for 48h. At the end of the 48-h period, participants returned to the laboratory and performed the test experiment for data collection. After a washout period of 7 days, the process was repeated with participants who had the high CHO diet previously, receiving the low CHO diet, and vice-versa (crossover design, Figure 2).
In the test day, participants arrived at 8:00 am in the laboratory after a 12-h overnight fast and rested on a chair during 20 min for the assessment of resting V̇O2 value (Quark b2, Cosmed, Italy). Then, they underwent a 5-min warm-up at 50 W, followed by an SE at 115% of V̇O2 peak until exhaustion, which was assumed when participants were unable to maintain the pedal cadence above 60 rpm. Immediately after the test, they sat comfortably on a chair for 60 min. The V̇O2 peak was measured continuously from the baseline to the end of the 60-min post-exercise period (Quark b2, Cosmed).

You have already seen the results of the O2 analysis (baseline values were similar for both groups) in Figure 1. So, I will stick to the results I haven't reported, yet:

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  time to exhaustion increases in the high-CHO group (4.4±0.6 vs 3.0±0.6 min, P=0.01, ES=2.4 large, power effect=0.98),
• total mechanical work was greater in the high-CHO group (76.9±16.5 vs 50.9±9.4 kJ, P=0.001, ES=2.0 large, power effect=0.91) and
• the V̇O2 measured at exhaustion was slightly higher in high- compared to low-CHO diet (48.6±11.0 and 45.2±11.0 mL·kg-1·min-1, respectively, P=0.004, ES=0.3 small, power effect=0.08)

To summarize it in the authors' words: "The high-CHO diet increased exercise duration (∼32%) and total mechanical work (∼34%) during a single SE bout. The increased tolerance further led to an increased exercise energy expenditure (i.e., ∼30% VO2 increase)" (Ferreira. 2016).
References:

• Ferreira, G. A., et al. "High-CHO diet increases post-exercise oxygen consumption after a supramaximal exercise bout." Brazilian Journal of Medical and Biological Research 49.11 (2016).