As I mentioned a few weeks ago, I heard a great presentation at the Metabolic Health Summit by Dr. Richard Johnson, a professor of medicine at the University of Colorado. In it, he talked all about fructose and its role in metabolic health.
I was intrigued enough to download his latest book, Nature Wants Us to be Fat (a copy of which I mistakenly almost signed at the author event) and I just finished it. It’s a fascinating read, pulling together research from zoology, laboratory mouse studies, and human biology to explore the phenomenon of weight gain, and attempting to pinpoint the drivers of the current obesity crisis.
the birds and the bears
It’s not just Winnie the Pooh that loves him some hunny. Bears in the wild go crazy for the stuff, along with something else sweet: berries. In fact, a black bear will eat up to 30,000 berries a day during the fall season, a time marked by what scientists call hyperphagia (literally, “over-hunger”). It’s as they are driven as if by instinct to eat everything in sight in order to fatten up for the winter. They then spend the winter in a state of “torpor,” (sounds familiar!) hibernating and living off the accumulated fat.
Berries and honey alike are marked by a high amount of the fruit-sugar known as fructose — as is nectar, the staple of hummingbirds’ diet. If you’ve ever owned a hummingbird feeder, you’ll know that those little sugar-fiends will hit that thing up nonstop throughout the season, and get more active in the late summer and early fall.
But hummingbirds don’t hibernate, you may be saying. It’s true that they don’t hibernate, but they do, in fact, migrate. Every year, these tiny fellas head from North America all the way to Mexico and Guatemala. In order to fuel that journey, they enter a hyperphagic state of their own, consuming their entire body weight in nectar daily. This fall feasting results in their nearly doubling in size, gaining enough body fat to fuel 600 miles of nonstop flying.
the fructose connection
The common ingredient in these animal kingdom pig-outs is fructose, and this is where Dr. Johnson draws some interesting theories. In his “fructose-survival hypothesis,” consuming large amounts of fructose tells the body that it’s time to store fat and slow metabolism in preparation for the coming winter. In several lab experiments on mice, he shows that eating fructose stimulates what he calls “the survival switch,” a biological response “characterized by hunger, thirst, foraging, weight gain, fat accumulation, insulin resistance, systemic inflammation and increased blood pressure.” Johnson’s lab has shown that fructose also blocks energy production (ATP) in the body’s cells, meaning a slower metabolism and less energy for things like exercise or activity.
This response is meant to be temporary and short-lived. It’s something that serves animals in the wild, where food is scarce and seasonal, and likely served us humans well in our hunter-gatherer days. But in our modern era of plenty — and especially when 60% of the foods in the American supermarket contain large amounts of fructose — our survival switch is permanently stuck in the “on” position and we can’t turn it off. This means we’re constantly over-hungy, driven to forage for extra calories (either in the fridge or at the mini-mart), and constantly over-tired, driven to veg on the couch rather than walk around the block or hit the gym.
The book goes into a great deal more detail about the survival switch, all while remaining very readable and engaging for the layperson like me. For example, he talks about how other things can also activate the switch, such as umami foods and dehydration, by prompting the body to produce its own fructose through something called “the polyol pathway.”
flipping the switch
All is not lost, however. The final part of the book outlines “The Switch Diet,” a set of guidelines on what to eat and what to avoid in order to flip your own switch out of survival mode. The advice is mostly familiar by now — cut out sugar, intermittent fast, eat more fish, avoid MSG, take a vitamin C supplement, and so on — but knowing the biology and science behind the recommendations makes it much more interesting.
Now, before I go, a few more fun animal facts:
whales don’t drink
In the early days of the Food Network, long before Bobby Flay was a household name, the young chef cohosted a low-budget outdoor cooking show called Grillin’ & Chillin’. For some reason, I revisited the old series recently through YouTube, and found an episode where his cohost, Southern barbecue guru Jack McDavid, describes how to find a fresh whole fish at your local market. Among his advice, the fish should have eyes that are “pretty” and lookin’ right back at you. “Sometimes it looks like the fish was drunk the night before — cloudy eyes, bloodshot… fish don’t drink!”
Well, it turns out neither do whales. You might think that the earth’s biggest mammal, who lives its life surrounded by water, gets its hydration from the ocean itself. Not so. In fact, most of their water comes from the food they eat. But they have a backup source: all that blubber. Fat burning within the body creates water as a byproduct, and this is what keeps the big guys hydrated during long months of migration.
The same is true of camels. When I was a kid, I saw a cartoon where the camel’s hump was filled with a water tank. Makes sense, I thought, and I’ve never really questioned it since. Turns out that big hump is actually filled with fat, which the camel burns for energy when crossing the dessert. And again, that fat-burning process produces water, which keeps it hydrated.
Whales and camels as the OG’s of keto and intermittent fasting. Who knew?
You shamed me into looking up umami - good news it’s a flavor in many foods I love to eat! To wit:
1. Seaweeds: Seaweeds like kombu and nori are low in calories but packed with nutrients and antioxidants. They’re also excellent sources of umami due to their high glutamate content. Kombu seaweeds are often used to add depth to broths and sauces in Japanese cuisine.
2. Soy-Based Foods: Soy foods, including tofu, tempeh, miso, and soy sauce, are made from soybeans. Fermenting and processing soybeans raise their total glutamate content. Soy-based foods have been linked to various benefits, such as lower blood cholesterol, improved fertility in women, and fewer menopause symptoms1.
Tomatoes: Ripe tomatoes are rich in umami flavor. Dried tomatoes, in particular, are potent sources of umami.
3. Parmigiano Cheese: This aged Italian cheese is famous for its umami richness. It’s often grated over pasta dishes or enjoyed on its own.
4. Anchovies: These small, oily fish are packed with umami. They’re commonly used in Mediterranean and Asian cuisines.
5. Mushrooms: Varieties like shiitake, portobello, and porcini are umami powerhouses. Add them to soups, stir-fries, or risottos for an extra savory kick
6. Cured Ham: Certain cured hams, such as prosciutto, offer a delightful umami flavor. Enjoy them thinly sliced or wrapped around other ingredients.
7. Cultured and Fermented Foods: Foods like cheese, soy sauce, and Worcestershire sauce are rich in umami. Fermentation enhances their savory taste.