Caloric Manipulation and Intermittent Fasting: Understanding Volume and Density

I touched on this topic in a prior post here:, but I wanted to spend a little more time on it because I’ve found it to be really important with respect to intermittent fasting.

I’ve mentioned in many prior posts that I practice a style of intermittent fasting (IF) that entails not eating for approximately 21 hours every day. This is my preference primarily because 1) it’s convenient not to have to think about food until the evening, a time when I can really enjoy it, 2) it produces a hormonal response favorable to retention of lean mass, and 3), it’s a really easy way to control calories.

For cutting fat, IF is a fantastic tool because it’s so easy to keep caloric intake well below maintenance. But there’s also another side to it: if you’re not careful with IF, you can end up squandering your hard work at the gym because it can be difficult to get enough calories in for muscle growth, especially if the eating window is very tight. I recently learned this the hard way when attempting to increase calories without regard for the energy density of the foods I was consuming.

Here’s what happened.

Last week I wanted to increase my caloric intake up to maintenance for a few days, so I figured I’d just eat more of what I normally eat. But I wasn’t at all thinking about the energy density of those foods. So in addition to the absolutely enormous salad I eat after my small dinner, I was pounding extra popcorn, then having an avocado banana protein pudding , then a huge bowl of oats and berries right before bed. My stomach was so astronomically full that I went to bed literally in pain on those nights. I also woke up with heartburn, a condition which I experience exceedingly rarely. My best guess is that I forced such a high volume of food into my body so quickly that the sphincters throughout my digestive tract couldn’t fully close, which might have allowed some digestive juices through to go places they shouldn’t have. With all that, I still didn’t hit my maintenance target.

The sliding scale: eating window vs. caloric density

There are two ways to address this issue. The first is to open the feeding window from three to, say five hours. But since I don’t like eating during the day, I prefer to keep my feeding window to around three hours. The second option is to eat more energy dense foods during the window while also reducing the intake of high volume foods. So now on days when I want to boost calories (like on lifting days), I decrease my salad size by half, replace popcorn with 1-2 servings each of cheese, nuts and eggs, replace the water in the avocado banana pudding with organic whole milk and add natural peanut butter to it, and replace the bowl of oats with a cup of ice cream (but NOT Ben and Jerry’s–something with less sugar per serving like Turkey Hill or Breyer’s). You probably realize that these foods are higher in fat; that’s where the energy density comes from. These are all low volume, high energy items that allow the intake of more calories while saving the stomach from splitting. While protein can also be great for curbing hunger, it’s not great from an energy density perspective. It’s not just the fact that a gram of it contains 4 kcal to fat’s 9, but it also requires far more energy to metabolize than fat or carbs, which further degrades its energy density.

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