Irish Superman: 4 Weeks of Potatoes

Back in May I mentioned that a study was recruiting participants to try a 4-week all-potato diet. What I didn’t say was that I was joining the study, and I finished this week.

I’m glad I did it; I lost 8 pounds and 2 inches of waistline, going from slightly overweight (BMI 26) to just barely not-overweight (BMI 24.9). Here are some of my notes:

Day 5: Energy boost kicked in today. Feel half my age

Day 6: Potato energy going strong. Feel like Irish Superman

Day 15: Almost too much energy, hard to sit down at a computer and work, took a break to play basketball

So like many people who previously tried this, I can add more anecdotal evidence of weight loss (despite eating all the potatoes you want) and energy. I’ll also echo people who said that “hunger feels different” and not as demanding, and that it “resets your tastebuds” so that previously bland foods taste good (I just had a turnip with zero seasoning and it was almost too intense). Now to answer your likely questions:

Q: Did you actually eat nothing but potatoes for 4 weeks?

A: No, but I got reasonably close. I cooked potatoes in avocado oil and added seasonings, I drank coffee and beer, I ate other vegetables, I had some snacks. Overall I estimate I got 75-80% of my calories from potatoes.

Q: Was it hard to stick to? didn’t you get bored?

A: Being hungry or even bored weren’t really issues, all 5 times I slipped up and ate a meal that wasn’t potatoes I’d say it was for social reasons (I was at a party with great food, at a restaurant with someone, et c)

Q: What kinds of meals did you cook?

A: Lots of home fries and roast potatoes using lots of varieties of potato (russet, gold, red, purple, sweet). Mashed potatoes a few times. McCain’s craft beer fries for my birthday.

Q: Aren’t potatoes bad for you? Why didn’t this make you fat?

A: Anything can be bad for you if you deep-fry it, or otherwise smother it with fats or process it to death. This is probably how most potatoes get consumed in America, but they start as nutritious root vegetables.

Q: What about protein? Doesn’t this kill your gains?

A: This was my biggest concern going into the study. Potatoes do have more protein than I thought, enough to live on but probably not enough to make you strong. My lifts did come down a bit, though it’s unclear if that was due to the lack of protein or just the lower calories and weight loss taking some muscle along with the fat. I was eating high-protein yogurt many days to try to mitigate this.

Q: If this is so great, are you going to keep doing it?

A: No, it was great for the first 14-16 days then just ok. Most of the weight loss and energy boost happened in the first half. If I ever do this again I’m going to plan on two weeks, which I think is also what Penn Jillette suggests. I do think I’ll do potatoes for lunch a lot more often than I used to, and pivot this to a “whole foods / not-ultra-processed” diet.

Q: Is there something special about potatoes? Would any single-food diet work as well?

I’m not sure. Some of the benefit likely comes from cutting out variety, so not eating a lot just because “I need to try everything”. Some likely comes from cutting out specific categories of food, like high fat / high sugar / hyper-palatable. I don’t think that just any food would work, probably most whole foods would, but potatoes are cheap and nutritious. The potato diet leading to weight loss is consistent with many, though not all theories of obesity.

Q: Can I still sign up for the study?

A: No:

Signups are now closed, but we plan to do more potato diet studies in the future. If you’re interested in participating in a future potato diet study, you can give us your email at this link and we’ll let you know when we run the next study.

But you can always just do it yourself.

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