Exercise doesn’t always cause weight loss. In his book, “Why we get fat and what to do about it”, author Gary Taubes cites several studies of exercise and weight loss. Some show modest weight loss, some show modest weight gain, some show no net change.
The studies seem to show that insulin resistant and type 2 diabetics (which are insulin resistant) tend to lose the most body fat from exercise.
I have both lost and gained weight from an exercise program. I originally used exercise years ago to lose 90 pounds. I then trained for a bike marathon and gained 8 pounds in 2 weeks. I suspect some of that may have been water since I was sweating and drinking a lot of water.
Exercise makes you hungry. Exercise also makes you tired and people sometimes will spontaneously move less between bouts of exercise which can have an impact on calorie expenditure. The body is complex and it’s not just eating less calories than burning. We have no way to accurately measure calorie burning at rest and our body can adjust our resting metabolic rate depending on how much we’ve eaten and exercised. We know that we feel more energetic after eating. We also know that if we exercise and restrict calorie intake, our body responds by making us feel hungry and tired.
The body also changes levels of our hormones that are responsible for water storage if we sweat a lot. Do a lot of exercise and sweat and your body will fiddle with your aldosterone levels to cause you to retain more water during periods of rest, in anticipation of future exercise sessions. Homeostasis.
The scale picks up changes in fat, muscle, water, and contents of your GI track. Some of that weight gain may actually be water and fecal matter (not to get too gross). I know my dumps are huge now that I am on Huel. I probably lost 2 pounds before and after my morning dump. Our typical American diets are low on fiber and an all-Huel diet contains a lot more than we are used to. It bulks up the contents of your colon. There’s a lot of weight in there.