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Exercise During Weight Loss- Should You or Shouldn't You?

News flash: There are many weight loss plans out there! Some are 500 calories with HCG shots, some are meal replacement without exercise, and some are intense exercise with meal plans, to name just a few! At Rainier Medical, the program is an evidence based medical protocol. Today’s blog is covering the important topic of exercise while on the 800 calorie a day meal replacement portion of the plan. This is crucial, because the type and amount of exercise significantly affects the results, tolerability, and durability of the results. What are the most frequently asked questions, the most common pitfalls, and what does the evidence/research show regarding exercise while on an 800 kilocalorie Very Low Calorie Diet?


Common Pitfalls.


  • Too Much Exercise

How is this possible? I thought exercise was good for weight loss, right? If a little is good, then more is better! Actually, intense or high volume exercise can inhibit weight loss. The cause is not entirely certain, but it is likely multifactorial, including the following:

- Inducing a stress response. This may release cortisol, which is an anabolic hormone. After all, when we evolved, if we were running a lot, we were probably in danger!

- Increasing hunger. Studies show that while exercise may have an anorectic effect to suppress appetite for about one hour following exercise, after that, calorie intake typically increases.

- Reducing non-exercise activity thermogenesis. This is a reduction in activity for the rest of the day following exercise. Basically, studies show that when people exercise intensely, they may be less active the rest of the day. The net increase in activity may then be zero.


  • Wrong Type of Exercise

Now, let me be clear, any type of exercise at any intensity at any time is “good” for you, in that it reduces the risk of cardiovascular disease and many other health conditions compared to not exercising, with all other things being equal. However, things are a little more complicated than that. Keep in mind your goal when you design your exercise regimen and be sure your exercise regimen is appropriate for that goal. The analogy that I use is that you will not exercise the same way all of the time. Think of professional athletes. They may train one way in the “off season”, then another way to peak for the season, and train a certain way to maintain during their peak “on-season.” Typically, the off season is used to make changes, in technique or body composition, and the on season is for performance. For a person on a very low calorie diet for the purpose of reducing weight, the exercise regimen recommendation is going to be different than someone at their goal weight training for performance.


  • Confusion Between Fuel, Recovery, & Nutrition

The obvious question is whether 800 calories a day is enough on which to exercise? If a person has a basal metabolic rate of 1600 calories a day and wants to perform 40 minutes of exercise and burn 300 calories, and is consuming 800 calories all day, where is that energy coming from? The Rainier Medical program induces a nutritional ketosis, when done properly, which means that fat tissue is converted into free fatty acids and used as fuel. For every 1 pound of adipose, there is about 3,500 calories of energy. So, if a person is losing 50 pounds of fat, that is 175,000 calories of energy. It can take 3-4 weeks for the muscles and body to fully adapt to using fat as fuel, so during that time, exercise capacity is typically reduced 25% on average from baseline, but may be more in individuals.

In maintenance, or not on a ketogenic meal plan, timing nutrition relative to exercise helps as well. Thinks of food in three categories: Fuel is the energy to perform exercise. Recovery is the energy and nutrients consume after exercise. Nutrition is everything else and is for maintaining body composition. In general, fuel is consumed about 90 minutes before exercise, recovery calories are within the 60 minutes following, and then nutrition is the remaining food in your daily budget.


The Evidence for Exercise During Weight Loss


This article studies 140 premenopausal women who lost an average of 25 pounds. They were split into three groups: those who did no exercise, those who did cardiovascular exercise, and those who did resistance training during weight loss. The study showed that following weight loss, the people who did no exercise during weight loss had a reduction in all three parameters measured: total energy expenditure, resting energy expenditure, and non-training physical activity energy expenditure, but not for the groups who exercised with either aerobic or resistance exercise. In the two groups who exercise, only the resting energy expenditure decreased (which is unavoidable, since the body weight was 25 pounds lower, on average, and resting energy expenditure is related directly to body weight). Either type of exercise prevented a reduced in resting energy expenditure during weight loss. Between the two groups who exercised, comparing those who did resistance training versus aerobic exercise, resistance training was shown to increase physical activity.


What is the punchline? During the active weight loss phase, I recommend the following:

  • During the first 4 weeks, exercise lightly, such as walking or light resistance exercise if you are already doing it. This allows your body to using fat as fuel. You should be able to perform 15-20 repetitions and speak in full sentences comfortably.

  • Exercise consistently during active weight loss in order to reduce the “slowing of the metabolism” that happens with weight loss.

  • Be sure your exercise program contains sufficient resistance exercise to prevent the reduction in resting metabolic rate and to increase physical activity outside of exercise. If you have more muscle and use it, your metabolism will be "faster."


As always, individualize and assess your program and your results in the context of your individual health, as there are always mitigating factors. These are generalize statements. Since there are many different body types, medical conditions, medications, etc, these are a starting point. The volume of exercise correlated with maintaining a 30 pound weight loss or more for 2 years or more is one hour per day. This is much higher than most people realize. So, it is necessary to build up a level of fitness over time just to be able to perform the volume of exercise needed to maintain a weight loss (without medications or surgery or meal replacements).


Target Heart Rate Training


Target heart rate training can provide objective feedback in the moment to guide the intensity of your workouts. The target heart rate ranges are based on your VO2 max. We used to perform this test at Rainier Medical prior to Covid. Some watches, like a Garmin, will estimate your VO2 max after you wear them with a heart rate strap for a while. I recommend exercising mostly in the 60-70% effort most of the time, with brief intervals into the higher 70% and occasional 80%. I find that exercising for too long at too high of an intensity is what triggers the hunger, fatigue, and impairs fat loss. Following are examples of my VO2 max and some heart rate tracings using a heart rate strap which we have at Rainier Medical and can use as part of our remote patient monitoring.









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