How often do you wonder about the best strategies to lose weight? A recently published study looks at the role of exercising in a fasted or fed state and aims to answer the question, “Do you lose more fat weight if you exercise in a fasting state (before you eat) or in a fed state after you eat?” In the end, the researchers say it doesn’t make any difference, but there are details that deserve discussion.
Researchers studied 20 non obese young active women attending a university. Some were off season track athletes, so the researchers matched the two groups based on weight and body composition, making sure the two groups included a comparable number of athletes. For four weeks the study participants were provided individualized meal plans with a 500 calorie deficit from their expected calorie needs using a standardized equation. In the meantime, the participants exercised for one hour three times a week at 70% VO2 max, which is typically considered a moderate level of exercise. Both groups lost weight and both groups lost fat with no significant difference between the two. So what deserves discussion?
WHAT DOES BODY WEIGHT AND BODY FAT MEASURES TELL US ABOUT METABOLIC HEALTH?
Researchers used body weight and body composition measures to match the participants in the two groups, but these measures aren’t sensitive enough to address fitness and metabolic status. We don’t really know anything about the participant’s relative metabolic health, just that they did not have any overt evidence of disease and they were not pregnant during the six months prior to the experiment.
The women reportedly consumed less than 1300 calories a day on average, but didn’t lose as much fat weight as the researchers expected. The authors speculated that possibly participants underestimated their food intake. I’m thinking there might be other explanations
13oo calories is achingly close to or could actually be considered semi-starvation for young active women, especially athletes. Many women chronically restrict calories without necessarily being diagnosed with an eating disorder. We call it “restrained eating”. Chronic calorie restriction leads to a reduced metabolic rate, sometimes measured by assessing one’s resting energy expenditure (REE). The researchers would have needed to assess each participant’s REE to know. Despite screening for healthy participants, it is possible that the energy expenditure equation used to determine calorie intake actually over-estimated the participant’s actual calorie needs. (And it is possible that everyone under reported their food intake as the researchers suggested.)
As I read this study I could already hear the soundbites for individuals who are looking to lose fat weight. Yet, data from some of the subjects could have skewed the results, making these findings less applicable to the rest of us. The off season track and field athletes involved in the study were known to have body composition levels at 11-13% body fat, basically at or below the essential body fat levels for women, and much lower than what many would consider fit or healthy. These women are already exquisitely lean. How does their participation in the study influence the data?
The researchers were careful to include athletes in both groups in order to avoid bias, which makes me curious about the range of weight and fat loss within each group. How did those athletes compare with everyone else in their respective groups? The average results reported don’t tell us nearly enough about the experience of all the different participants. I wrote to two of the authors, and both wrote back without answering my questions. So I guess we don’t get to know for now. With so little body fat to lose, the athletes could have diminished the average results seen with more typical young women seeking weight loss.
WHAT ABOUT THE ACTIVITY
All the participants exercised at 70% VO2 max, but that doesn’t mean all the participants exerted the same effort to accomplish this task. I am curious if the athletes experienced a different level of perceived exertion–and a different metabolism of fat and carbohydrate while exercising at the same intensity. In addition I would like to know if that activity exerted any impact on the participants sense of hunger and satiety during the rest of the day. Too often researchers are preoccupied with collecting data and forget to ask the participants about their experience throughout the research protocol.
WHAT ABOUT THE FOOD
The participants of both groups consumed close to 50% of calories from carbohydrate and the rest of the calories split between protein and fat. But the beverage given to the fed participants before exercise measured 25o calories with 40 grams of carbohydrate–about 65% of the calories from carbohydrate. Some people burn fat better when they eat less carbohydrate. I wonder if the experience would have been different for the fed group–or any individuals in the fed group–with a pre-workout beverage yielding a protein-carbohydrate-fat ratio closer to the average intake.
The bigger question remains, would a more individualized approach to diet be more effective for each individual and the group results. Researchers continue to seek the holy grail of diets: which one works best. That’s the wrong question. We need to be looking for ways to determine what diet works best for any one person.
MOVING TOWARDS PERSONALIZED NUTRITION PRESCRIPTION
Despite trying to answer a singular question, this study mostly triggers more questions: What was the experience of each participant? What does the range of measured change tell us about the range of possibilities within the study group?
Years ago when I worked much more frequently with athletes, I soon adopted a “personalized” approach to nutrition counseling. The unique needs, training and demands of athletes at different ages, in different sports and more critically with different genetic and environmental factors influencing metabolism basically taught me to individualize everything. Research continues to rely on randomized study protocols that assess average results in order to achieve statistical significance. This framework often misses important differences between subjects and leads to broad recommendations based on averages. Most studies, including this one, fail to report or explore the range of outcomes measured by the different participants exposed to a specific dietary and exercise protocol. I’m left wondering if studies like this could offer much greater perspective by reporting all the outcomes, not just the averages.