Recently an article was published in the May, 2012 issue of the IDEA Fitness Journal trade magazine entitled Eating or Fasting For Fat Loss: A controversy Resolved, by Dr. Len Kravitz PhD.”
First, let me say I’m a big fan of Dr. Kravitz, however, I do have some questions and comments in regards to his article.
In the study, he had eight men who didn’t eat breakfast before they trained but a “normal” breakfast after their workout and then had the same eight men eat a 673-calorie Mediterranean breakfast before training to see which version burned more fat during the day by fasting or not fasting before a workout.
1. There were only eight “trained” men with an average height of 70 inches and weighing 207 pounds. At 5’10 and 207 pounds how were they “trained?” He never mentions their lactate threshold. Why is this important? Although he had the volunteers do a 36-minute cardiovascular workout on a treadmill at 65% of the heart rate reserve, it doesn’t tell me everything I need to know. For example, an aerobically trained athlete won’t go anaerobic until 90+% of the heart rate reserve so at 65% this kind of athlete wouldn’t be perceiving much intensity, therefore the post exercise consumption (EPOC) wouldn’t be much since EPOC increases because of intensity. An aerobically trained athlete wouldn’t be burning much sugar at that intensity either. I would have liked to have seen this data to help get a picture of what kind of aerobic fitness level these eight subjects had. I don’t have many male clients that are 5’10 and 207 pounds.
2. In a chart, Dr. Kravitz demonstrates the post exercise oxygen consumption at the 12-hour and the 24-hour mark. The chart shows the eight subjects burned slightly more calories because they had a higher EPOC and a lower RER (Respiratory Exchange Ratio). As RER rises the body uses more carbohydrate for its energy needs. In essence, the article misleading leads us to believe they were burning more calories but the calories were not from sugar which I will explain better below. I would’ve liked to see the rest of the math. Although, their EPOC was higher, they did eat 673 more calories for that day. Did the 673 calories offset the higher EPOC? At the end of the day, did the subjects end up in a caloric deficit? Did they lose body fat? In the fasting week, the subjects ate a “normal” breakfast after the workout. The caloric intake for that breakfast was never defined, so we don’t know the total daily caloric intake for both groups.
3. According to the chart, there was only a .3 ml O2/kg/min difference between the groups at the 12-hour mark and even less at the 24-hour mark! Although the RER was slightly higher (and I mean slightly) in the fasting group workouts, both of the groups were burning a mixture of carbohydrates and fat. An RER of 0.70 indicates that fat is the predominant fuel source, RER of 0.85 suggests a mix of fat and carbohydrates, and a value of 1.00 or above is indicative of carbohydrate being the predominant fuel source. The RER for the non-fasting week was 8.0 at 12 hours and 8.25 and 24 hours while the fasting group was at 8.25 and 8.75.
Without knowing the rest of the math, I don’t disagree that the controversy is “busted” or resolved.