Why whole apples are more filling than apple juice

HostI was at the store the other day looking at those big bottles of apple juice. It takes about four or five apples to fill one small glass, and I realized I could drink that whole thing in a minute. If I tried to eat five apples in a row, I would be stuffed before I even finished the third one. What's it about the whole fruit that actually keeps us from reaching for more?

GuestIt really comes down to how our bodies handle speed. Think about what happens when you take a bite of a crisp apple. You have to use your teeth, you have to chew, and you have to swallow small bits one at a time. That whole way of eating takes a few minutes. While you're busy crunching, your brain is getting a steady stream of signals from your mouth and your throat saying that food is on the way. By the time you finish that one apple, your brain has had time to catch up and realize you're eating. But juice is like a fast-forward button. You can drink the sugar and the energy of five apples before your brain even knows you have started. There's no chewing to slow you down, so the signal that tells you that you're full never gets a chance to fire off.

HostBut if I just blended the apple into a smooth drink, it's still the same fruit, right? The bits are all still in there. It seems like it should work the same way in my stomach.

GuestYou would think so, but even blending changes things. The fiber in a whole apple acts like a mesh or a cage. It holds the sugar inside these tiny, tough walls. When you eat the apple whole, your body has to work hard to break those walls down to get to the sugar. It’s like a slow leak. When you juice an apple, or even blend it at high speed, you rip those walls apart. All the sugar is just sitting there, free and clear, ready to rush into your blood all at once. Without those walls to slow things down, your body gets hit with a huge wave of sugar that it wasn't expecting.

HostSo even if the calories are the same, my body is seeing two totally different things. A calorie is just a unit of energy, so why does the body care if it comes in fast or slow?

GuestOur bodies aren't just tanks we fill with gas. We have sensors everywhere. When all that juice hits your stomach, it doesn't take up much space. It's a heavy liquid, but it passes through the exit of your stomach and into your gut very quickly. A whole apple is different. It's bulky. It has shape. It stays in your stomach longer because it's harder for your gut to turn it into the liquid soup it needs to be. While it sits there, it physically stretches the walls of your stomach. Those stretch marks send a very clear message to your head that says we're full, you can stop now. Juice just doesn't put that same pressure on the walls. It's in and out before the sensors can even do their job.

HostThat makes sense for the stomach, but I also feel like juice gives me a quick rush and then I feel tired. Does that crash play a part in why I want to eat again so soon?

GuestIt plays a huge part. Because that juice hits your system so fast, your blood sugar levels go way up, almost like a spike. Your body sees this and it kind of panics. It lets out a chemical called insulin to clear that sugar out of the blood as fast as it can. The problem is, it often works a little too well. It clears out so much sugar that your levels crash back down lower than where they started. That crash is a big signal to your brain that you need more energy right now. So, even though you just had the energy of five apples, your brain is screaming for a snack ten minutes later. With the whole apple, the sugar enters the blood in a slow, steady crawl. You don't get that big spike, so you don't get the big crash. You just feel steady and satisfied for a much longer time.

HostI’ve heard people say that juice is basically just soda without the bubbles. That feels a bit mean to fruit, but is there some truth to it when we look at how the body reacts?

GuestIn terms of how fast the sugar hits your blood, they're actually very similar. When you take away the fiber and the chewing, you're left with water and sugar. Now, juice does have vitamins that soda doesn't have, so it's better in that way, but your liver doesn't really know the difference. When it gets hit with a big load of fruit sugar all at once, it has to process it fast. If it gets more than it can handle, it just starts storing it as fat. The whole apple avoids this because it doles out the sugar in small doses. It gives your liver time to keep up. It's like the difference between a nice, steady rain that soaks into the garden and a flash flood that just runs off and causes trouble.

HostIt's wild that just changing the shape of the food can change how our organs work. It sounds like the apple is doing a lot of the work for us just by being tough to eat.

GuestThat's exactly it. We evolved to eat things that are hard to break down. Our bodies expect us to work for our food, to chew it and wait for the stomach to do its job. When we do the work for the body by juicing or blending, we skip all those natural speed bumps. Scientists did a study where they gave people whole apples, apple sauce, or juice. Even though the energy was the same, the people who ate the whole fruit felt the most full and they actually ate less at their next meal. The juice drinkers felt the hungriest. It shows that the way food is built matters just as much as what's inside it.

HostThe fruit juice is really just an apple with the brakes taken off.

GuestThose five apples go from a full meal to a quick sip that leaves you looking for more.

HostThe bottle of juice might look easier, but it seems like our bodies prefer the crunch and the slow crawl of the whole fruit to keep things steady.