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?

Rat Study: High Carb Diet Induces Hepatic Steatosis and Increases Heart Fat by 43%

For a large part of the 1980s and 1990s fats have been considered the "source of all evil". Now, it is our carbohydrate consumption which is held to be responsible for diabetes, obesity and the other ugly faces of "the metabolic syndrom". A recent study by a group of scientists from Sao Paulo (Haubert. 2010) seems to confirm this "revised" hypothesis.

Over a period of 21 days, the scientists fed a group of rats (experimental) a 70% carbohydrate diet with astonishing or rather shocking results (cf. table 1)

 

Within three weeks the rats developed a fatty liver and their heart fat mass increased by 43%. While the scientists did not provide much information about the overall underlying mechanism of these changes, they emphasize the pronounced decline in tissue vitamin E produced by the high carb consumption. In how far additional vitamin E may have prevented some of the fat accumulation yet remains unknown and would warrant further investigation.

Dieting: Nutrient Composition Probably Less Important than On-Going Low vs. High Carb Debate Suggests

In a soon to be published study Kerksick, et.al. (Kerksick. 2010) investigated the effect of 6 dietary regimens on weight loss in 141 obese women (38.7 +/- 8.0 yrs, 163.3 +/- 6.9 cm, 93.2 +/- 16.5 kg, 35.0 +/- 6.2 kg*m-2, 44.8 +/- 4.2 % fat). Interestingly, the members of all groups with restricted dietary intake + exercise achieved similar rates of weight loss (cf. Figure 1)

Figure 1: Changes in weight for High Energy Diet (HED), No Diet (ND), Very Low Carbohydrate High Protein Diet (VLCHP), Low Carbohydrate Moderate Protein Diet (LCMP), High Carbohydrate Low Protein Diet and no diet + no exercise Control (CON)

What I consider most important, though, is the statistical spread of the results. For me this confirms what I have been telling people over and over: There is no "one solution fits it all", it is quite obvious that - from a metabolic point of view - the low insulin level on low carb diets is a major plus (I am a low, but not no-carber, myself). Eating little to no carbs, on the other hand, just does not work out for some, so that they may eventually end up gaining weight instead of losing it (cf. Figure 1).

Bottom line: If you want to lose weight (not fat if you are already lean), eat less calories than you need, exercise and make sure you get proper amounts of nutrients (protein, fats, vitamins and minerals).