You can't maximize weight loss and fitness at the same time. This is a proven fact.
The fastest way to lose weight is on a medically-supervised very low-calorie diet (VLCD). On a VLCD, patients consume 800 calories per day, which is the minimum amount of energy the average person can take in without damaging his or her health.
It is possible to do some light exercise on a VLCD, but as you can imagine, you can't exactly train for a marathon.
Weight Loss vs. FitnessThat's an extreme example, but there are less extreme examples that also show you can't maximize weight loss and fitness at the same time.
For example, in 2009 researchers from Southern Connecticut State University separated 34 cyclists into three groups. One group added sprint intervals to their training. A second group went on a weight-loss diet. A third group did both. The researchers who conducted the study were interested in comparing the effects of these three interventions on the cyclists' power-to-weight ratio, which is one of the best predictors of race performance capacity on a bike.
The results were interesting. It turned out that the power-to-weight ratio improved in the group that did sprint intervals without dieting and in the group that dieted without doing sprint intervals, but it did not improve in the group that did both.
Why? The authors of the study speculated that the reduced calorie intake of the weight-loss diet prevented these cyclists from gaining any power from the sprint intervals.
Importance of FuelingThe lesson is this: When you're training for a marathon or other important race, you need to fuel your body for maximum performance in workouts and maximum recovery between workouts. This approach to nutrition during the training process will necessarily limit the amount of weight you lose.
Most runners lose some weight when training and eating appropriately for an important race, and some runners even lose a lot of weight. But you can't expect to lose as much weight as you would if weight loss were your highest priority, rather than maximum fitness.
A Time for EverythingThere is a time to make weight loss your highest priority, but it's not while you're focused on an upcoming race. The best time to pursue faster weight loss is right before you start formally training for a big race. I call this short period of emphasis on weight loss a quick start.
I recommend quick starts for all runners who are more than five pounds above their optimal racing weight when they're getting ready to start training for a big race. Focusing on weight loss for 4-8 weeks before the race-training process formally begins will enable most runners to reach their ideal racing weight in time for their race without having to compromise their fueling (hence their fitness) during the training process.
Your diet and training within a quick start should differ from your diet and training during the training process in five key ways:
1. Moderate Calorie DeficitDuring a quick start you should aim to consume 300-500 fewer calories per day than your body would need to maintain its current weight. This deficit is sufficient to yield fairly quick weight loss, but would be too large within the race-focused training process, when you need your diet to support heavy training for an upcoming race.
2. Strength TrainingA quick start is also a good time to make a greater commitment to strength training than you do at any other time. I recommend three full-body strength workouts per week at this time. This will help you lose weight by adding muscle mass to your frame and thereby increasing your metabolism, so you burn more fat at rest. Building strength during a quick start will also help you run better and stay injury free during the subsequent race training process.
You won't have as much time and energy to lift weights within the training process, when you're running a lot more.
3. Increased Protein IntakeI recommend that runners aim to get roughly 30 percent of their daily calories from protein during a quick start. There are two reasons for this recommendation.
First, high-protein diets are more filling than moderate- and low-protein diets. So increasing your protein intake during a quick start will help you maintain your daily calorie deficit without hunger. Second, increased protein intake will help you build muscle through strength training.
Within the training cycle your protein intake needs to be lower to make room for increased consumption of carbohydrate, your most important endurance fuel.
4. Sprint IntervalsA quick start is not the time for high-volume endurance training. That should wait until you're within the race-focused training process. High-volume endurance training promotes fat loss. So if you're not going to do it during a quick start, you have to promote fat loss through training in other ways.
As we've seen, strength training is one way. Another is sprint interval workouts. Training sessions consisting of large numbers of very short (10-30 seconds) sprints are proven to promote significant fat loss, especially between workouts. They also develop power that will help you get off to a good start when you move into race-focused training.
This is not a type of training that you can do much of within the race-focused training period, when more race-specific types of workouts must be prioritized.
5. Fasting WorkoutsA fasting workout is a long, easy run undertaken in a glycogen-deprived state. This means you don't eat before you start and you don't take in any carbs along the way. This forces your body to rely on fat to fuel the workout, making it a great fat-burning session.
I advise runners to perform one fasting workout per week during a quick start. Later, when you're actively training toward a race, you should consume carbs before and during most of your long runs to maximize your performance in those workouts.
Matt Fitzgerald's latest book is Racing Weight Quick Start Guide: A 4-Week Weight-Loss Plan for Endurance Athletes.