Want to Burn More Fat During Your Cardio Training? Eat Low Carb Before Workout!

Modulation of substrate utilization is the key to effective weight loss. For years we have been told that "training in the zone" (referring to a specific heart rate) would do the trick - recent research does yet suggest otherwise: High Intensity Interval Training (HIIT) has been shown to be at least as effective in burning off unwanted body fat, as the longstanding "gold standard", Low Intensity Steady State (LISS) in the "fat burning zone".

Researchers from the Department of Exercise Science and Sports Studies at Springfield College, Springfield, MA, USA, have now found that apart from the type of exercise you chose to perform, the nutrition, especially in the hours before working out, determines whether you will predominantly burn fat or carbs to sustain the workout.

In their study (Gregory. 2011), Gregory et al. compared the metabolic responses of a group of 8 "active, pre-menopausal" women to a 30 minute exercise regimen performed after either a low carbohydrate (LC: 392 kcal @ 15% carbohydrate, 68% fat, and 18% protein) or a low fat (LF: 396 kcal @ 78% carbohydrate, 7% fat, and 15% protein) meal. Respiratory gas exchange (RER), blood glucose (G), insulin (IN), triglycerides (TG), and free fatty acids (FFA) were measured. While "no significant differences existed between test meals for fasting blood measurements", the post-exercise results showed significant differences:

Postexercise (PE) FFA (mEq·L-1) levels were significantly greater following LC [1.1 (0.3) vs. 0.5 (0.3)]. PE TG (mg·dL-1) levels were significantly greater following LC [152.0 (53.1) vs. 114.4 (40.9)]. RER was significantly lower at all time points following LC compared to LF.

With the respiratory gas exchange being a measure of the relative contribution of fatty acids to fulfill the exercise-induced energy demand (Chessex. 1995), the researchers rightly conclude "ingestion of a single LC meal resulted in greater lipid oxidation at rest and during exercise as compared to a single LF meal." But, let's be honest - did you expect anything else?

Glycogen-Depleted Athletes may Benefit from 0.3g/kg BCAA Supplementation: Improved Endurance & Lipid Oxidation

If you have ever read up on the general recommendations concerning "cardio on an empty stomach" you will most likely have encountered the advice to supplement with branched-chained amino acids (BCAA) before or in the course of the workout. I have always considered this to be a solid advice, up to now, I had yet not seen a study underpinning the common sense reasoning behind the suggestion.

Now, Gualano et al. (Gualano. 2011) published a study that investigated the effect of BCAA supplementation on exercise performance and energy metabolism in glycogen-depleted athletes (let's assume by now that an athlete following a low carb diet is in fact glycogen-depleted when he wakes up). In a double-blind placebo controlled fashion the scientists provided their subjects with either 0.3g/kg BCAA or placebo for 3 days...

On the second day, subjects were submitted to an exercise-induced glycogen depletion protocol. They then performed an exhaustive exercise test on the third day, after which time to exhaustion, respiratory exchange ratio (RER), plasma glucose, free fatty acids (FFA), blood ketones and lactate were determined. BCAA supplementation promoted a greater resistance to fatigue when compared to the placebo (+17.2%). Moreover, subjects supplemented with BCAA showed reduced RER and higher plasma glucose levels during the exhaustive exercise test.

For all of you who are now asking themselves, what validates the claim of increased fatty acid oxidation, its the reduced respiratory exchange ratio. Although its arguable how reliable a measure the ratio between O2 in and CO2 out is in terms of fatty acid metabolism, these results support the hypothesis and real world observation that BCAA-supplemented cardio on an empty stomach reliably promotes fat loss.