What role does exercise play in a low carb lifestyle?

The answer to that question is: "it depends".

First, we need to clarify whether your goal is weight loss or maintenance.  If you are planning to lose weight, we need to look at exercise very differently than if you are trying to maintain weight.

Think about it....

If you are trying to lose weight on any type of diet, you are restricting your dietary intake (i.e. calorie intake).  In a low carb diet you are restricting your carbohydrates as well. If you are restricting your carbs to the degree that you are in nutritional ketosis, you will be burning fat for fuel and in theory, should have an endless supply of energy since all of us (even skinny folks) have more fat stores than glycogen stores for fuel. Seems logical that we could endlessly exercise and lose weight, efficiently burning off as much fat as we want, doesn't it?

The problem with theory is that there are always complicating factors that are not anticipated. The problem with endless exercise on any diet is that we become VERY HUNGRY when we rapidly burn calories. How do we manage exercise AND hunger? Simply put, most people just eat too much.

During weight loss, sustained, cardio or aerobic exercise beyond 20-30 minutes, will produce a SIGNIFICANT amount of hunger!

Most people cannot avoid eating after burning off hundreds of calories. It takes a very strong will to do so. Even in nutritional ketosis, there can be uncomfortable hunger with excessive cardio exercise.

The best exercise during weight loss to avoid hunger and resultant consumption of too many calories that will tank our weight loss efforts, is resistance training:  such as lifting weights, use of stretch bands, free weights, yoga, pilates, or use of one's own body for a resistance work out, with the idea of BUILDING MUSCLE FIBER WHICH INCREASES THE BASAL METABOLIC RATE.

Building "a bigger machine" (building muscle mass) will burn more calories while we are at rest doing nothing, than without adding more mass. That does not mean adding fat mass, but specifically must be the addition of  muscle mass. Many diets cause muscle wasting with the exception of diets that are replacing and/or adding sufficient protein to avoid it's loss. That is why a low carb, moderate protein, high fat diet is so beneficial!  

Muscle wasting is not likely to occur in this type of diet. Building additional muscle mass will assure more efficient weight loss since there will then be a larger difference between calories burned at rest and calories consumed.

*Remember:  If your choice of exercise drives you to eat more,  you will not lose weight!

If you are trying to maintain your weight:

Both aerobic and resistance training are beneficial.  

Our muscle cells are more receptive to the effects of insulin with this type of exercise. Aerobic exercise is also important for cardiovascular system health (blood pressure, more efficient cardiac output), as well as providing great stress relief.   Resistance work (building small muscle fibers) still has the same role as in weight loss.

If we burn hundreds of calories with aerobic exercise and are not trying to lose weight, we can afford to eat more from the hunger that results from it. While losing weight, we can't.  After any exercise, it is best to have a protein based snack for better muscle recovery, and to maintain good hydration.

Drink at least 64-96 ounces of water every day!

To summarize:

1)  Exercise is very beneficial to us for many reasons, but during weight loss, the aerobic/cardio training should be less than 30 minutes per day (for some people 20 minutes if getting too hungry).

2) During maintenance of weight, both aerobic/cardio and resistance training (lifting weights, etc) are important.

Best practice of resistance workouts when using free weights, resistance bands, or circuit machines in a gym:

The weight or resistance should be heavy enough to only do 8-12 reps at a time, sets of 3.

If you can do 20 repetitions, you are toning muscle and won't be building any muscle.  We are not trying to accomplish having you look like the Incredible Hulk here, just building a small amount of muscle for definition and more muscle mass to boost your metabolic rate.