The dark side of optimizing your metabolism

This is Optimizer, a weekly newsletter sent every Friday from Verge senior reviewer Victoria Song that dissects and discusses the latest phones, smartwatches, apps, and other gizmos that swear they’re going to change your life. Optimizer arrives in our subscribers’ inboxes at 10AM ET. Opt in for Optimizer here.

In the last few years, I’ve seen an increasing number of wellness and fitness influencers yap about fixing their metabolisms. For some, that means hawking supplements like Foodology’s Coleology Cutting Jelly, NAD+ pills for improving insulin sensitivity, or powders that claim to “balance your hormones.” Right now, my TikTok FYP is full of girls talking about the viral Korean Switch-On diet — a seemingly brutal regimen of intermittent fasting, protein shakes, and tofu. An obesity researcher purportedly designed the diet, which will “reset your metabolism.”

It’s easy to scroll past these diet fads. What strikes me is the verbiage. “Optimizing your metabolism.” What’s even the goal behind that? And where my alarm bells start ringing is when the algorithm mixes in a video of an influencer talking about optimizing their metabolism using continuous glucose monitors (CGMs).

CGMs are tiny wearable devices that measure glucose levels in the interstitial fluid just beneath your skin. They’re life-saving devices for diabetics, and now that they’re available over the counter, they can be helpful tools for folks with prediabetes and Type 2 diabetics who aren’t dependent on insulin. Their usefulness here is undeniable.

A larger question — and one I’ve been investigating for over a year — is whether there are tangible benefits for people who aren’t diabetic or prediabetic. I’ll be doing a deep dive into that soon, but right now, let me tell you how using CGMs this past year nearly wrecked my relationship with food.

I think a lot about food before any holiday. Some years, that’s all I think about. But not in a fun, “Oh, I can’t wait for a bite of stuffing or pumpkin pie!” kind of way. Think more of a hellish “What will I allow myself to eat?” or “Is there a race I can sign up for to mitigate the damage?”

I hardly think I’m alone in that. Whether it’s for weight loss or to manage a condition, anyone on a diet will tell you that holiday feasts can be a major source of anxiety. Partaking in the deliciousness can trigger waves of guilt, particularly if you struggle to manage portions. Personal discipline isn’t always a good thing, either. I’ll never forget the hurt look on my mom’s face when I declined a slice of the Junior’s cheesecake she’d bought just for me one Christmas.

I wore a CGM to Thanksgiving dinner last year. My relatives were curious, but cautiously supportive. But I noticed I was reluctant to eat certain foods, aware of how they might spike my glucose. Normally, I enjoy mashed potatoes with gravy. I love Ocean Spray canned cranberry jelly with my entire being. Sweet potato casserole with marshmallows is glorious. To make my spouse feel welcome, my Korean family had even baked a pretzel salad — an unholy Southern concoction of Cool Whip, cream cheese, frozen strawberries, crushed pretzels in butter, and Jell-O. (Yes, my in-laws insist it’s a “salad” and serve it as an entree, not a dessert.)

Instead of heaping my plate with my favorites, I had a half plate of actual salad, dressing on the side, a quarter plate of protein, and a single slice of canned cranberry jelly. I nursed half a glass of wine the entire night. When my aunt despaired, prodding me to eat more, I checked two separate CGM apps to see if I could swing a second plate. I argued with myself in my head. Maybe I could? I’d run my customary Turkey Trot that morning, and even though I’d treated myself to one of Wawa’s Gobbler Bowls after, it had only cost 620 calories and caused a modest glucose spike. I’d walked into dinner with a borderline low glucose level. Maybe I could offer to run an errand and sneak in a 10-15 minute walk before leaving?

Then, in the morning, I wouldn’t have to rationalize a less-than-favorable summary as a “holiday one-off.” I could safely say I’d had a “healthy” Thanksgiving. Doctors often recommend loading up your plate with leafy greens, prioritizing protein and fiber, and limiting processed sugars. All things I did. I’d been training regularly and ran a 5K that morning. Walking after meals has been shown in research to boost your metabolism significantly. Limiting alcohol is good.

I had half a second plate, mostly to soothe my aunt, and left half my dessert. My glucose charts looked good at the end of the night. I resolved to do better at Christmas. True to my word, I did the same exact thing a month later. And on my birthday. For the latter, I didn’t let myself eat cake.

A year later, I’ve had time to reflect. On the surface, I crushed the holidays last year. In reality, I didn’t enjoy a single bite. I didn’t appreciate the effort my family had put into a home-cooked meal. I don’t even remember much of the time I spent with my loved ones — my brain was too preoccupied with my glucose levels. And for what? After all these months, was my metabolism truly optimized?

Ironically, after losing about 15 pounds pre-CGM testing, I started gaining weight. I found myself skipping meals, particularly breakfast, more often. It was frustrating to deny myself the occasional dessert or after-dinner snack and still wake up with higher-than-ideal glucose levels. I found ways to avoid eating out or socializing. It wasn’t until my running performance started truly tanking that I realized I was relapsing into old disordered eating habits — ones I’d worked so hard to kick and had returned so stealthily. Things weren’t adding up. I set up a doctor’s appointment soon after. Two months and several tests later, we’re still trying to figure out why my metabolism isn’t operating as it should and how to address it.

This isn’t a categorical dismissal of CGMs. Like any wearable, they’re a tool. I wholeheartedly believe that many people — particularly self-quantifying nerds and people embarking on lifestyle changes — may find them helpful. Arguably, that I’m working with my doctor to find a successful treatment is a positive outcome.

We have to think critically about when, how, and by whom these tools are used. CGMs could help many non-diabetics. They will also inevitably harm some people. It’s why I reacted so viscerally when, earlier this year, health secretary RFK Jr. suggested that every American ought to use wearables, specifically highlighting CGMs as a means of “taking responsibility” over their health. The sense that these gadgets are backed by scientific research adds another layer of complexity. Yes, there’s a strong scientific basis. Yes, CGMs can be powerful tools. But they aren’t a panacea for any and every metabolic issue.

I’m lucky and self-aware enough to recognize when the tools are using me. And yet, it still took me months to realize that I’m not someone who can healthily use CGMs during holidays. That, for me, optimizing my metabolism isn’t something I can just do with a gadget. That all my expertise in this space doesn’t make me immune to health anxiety.

By the time you read this, I’ll have already run a Turkey trot and eaten Thanksgiving dinner. I won’t have worn a CGM. I suspect I’ll have struggled a bit when loading my plate. But, I’m also hopeful that I’ll have eaten two slices of my canned cranberry jelly and enjoyed every bite.