Where the praties grow: My seven-day potato diet experiment

I recently finished the book Potato: A history of the propitious esculent.  In it, John Reader takes his audience on a meandering tour of the potato’s history, ranging from academic explanations of the potato’s role in early industrial labor markets to folksy accounts of his time living in rural Western Ireland.  I quite enjoyed it.

One of the things that fascinates me about potatoes is their nutritional near-completeness.  Cultures in the Andes subsisted mostly on potatoes for thousands of years, building vast civilizations, and the Aymara and Quechua still eat such a diet today.  In 18th and 19th century Ireland, the average person’s diet consisted almost exclusively of potatoes, often with the buttermilk that was left over after butter was sold for income.  Despite abject poverty due to crushing oppression by the English, by all accounts the Irish during this time were in excellent health and had the highest fertility rate in all of Europe.  On page 157 of the paperback, Reader quotes farmer and Royal Society fellow Arthur Young, who conducted a survey of Irish agriculture in 1776-9:

I have heard [the potato] stigmatized as being unhealthy, and not sufficiently nourishing for the support of hard labour; but this opinion is very amazing in a country, many of whose poor people are as athletic in their form, as robust, and as capable of enduring labour as any upon earth.  When I see the people of a country, in spite of political oppression, with well-formed vigorous bodies, and their cottages swarming with children; when I see their men athletic and their women beautiful, I know not how to believe them subsisting on an unwholesome food.

From page 148:

The population of Ireland more than doubled between 1687 and 1791, rising from 2.16 million to 4.75 million.  During the fifty years from 1791 to 1841 another 3.4 million were added, taking the population to 8.15 million.  Another 1.75 million emigrated to North America, Scotland, England and even Australia during the same period, which brings the total born in Ireland to nearly 10 million — almost a five-fold increase in 154 years (1687 to 1841). ‘Probably in no other western country has so rapid a rate of natural increase been so long sustained,’ writes the historian Kenneth H. Connell.

This book, coupled with a few other influences, inspired me to try a mostly-potato diet for a week.  This inspiration happened to coincide with our recent harvest of 1,500 pounds of potatoes from a garden we share with another couple.  Here’s a photo of our largest potato, a freshly unearthed Cal White that weighed nearly four pounds:

We’re proud parents of this baby-sized potato.

This potato would have flabbergasted farmers in 18th-century Ireland, where a four-inch diameter potato was considered unusually large (p. 148).

My wife and I chose to eat a slightly more affluent version of the 18th/19th-century Irish diet: baked or microwaved potatoes, homemade whole milk yogurt, and salt to taste.  We also supplemented dinner with a portion of vegetables tossed in a little olive oil or vinaigrette.  I occasionally had a snack of dried fruit, and one day I had a non-potato lunch with a friend.

This resulted in a diet that was higher in carbohydrate and lower in fat than my typical fare, and also very low in reward value.  I knew it would be hard to eat enough calories so I made an effort to stuff as much down as possible.

The first few days were, honestly, rough.  Although I wasn’t hungry, I felt mentally foggy and shaky between meals, which eating a bit would correct.  My exercise tolerance was terrible and I had to scale back my cycling and strength training routine.  My wife felt the same way.  Interestingly, this reminds me of a phenomenon people talk about called the “low-carb flu”.  I’ve never experienced this, but many people report that in the initial adjustment period to a very-low-carbohydrate diet, they feel foggy, tired, cranky, and have low exercise tolerance.  I wasn’t expecting this to happen with potatoes, but perhaps it occurs whenever the body has to adjust to a substantially different macronutrient composition.

As the week went on, I gradually felt better, and by day five I was no longer feeling foggy or shaky between meals and my exercise tolerance had bounced back.  In fact, on day five I went for a jog and ran faster, and with less effort, than I can remember running in a long time.  My wife also felt better as the week progressed.

After a few days on the diet, non-potato foods began to taste fabulous.  I always enjoy fresh vegetables from my garden, but while I was on the potato diet, simple tomato or lettuce salads with vinaigrette dressing were delectable.  Despite that, potatoes and yogurt never became unappealing.  The diet was certainly monotonous, but not unpleasant.

My weight was stable over the course of the week, and my digestion was brisk.  I experienced very little hunger between meals.  The experiment would have been more informative if I had continued for longer, but it would have been challenging for social reasons and I didn’t have a compelling reason to do so.

In parting, I’ll leave you with these verses from a traditional Irish folk song, as printed in Potato (page 151):

Says I, ‘My lovely darling I’m tired of single life
And if you’ve no objections I will make you my sweet wife’.
Says she, ‘I’ll ask my parents and tomorrow you shall know
If you’ll meet me in the garden where the praties grow’.

Her parents they consented and we’re blessed with children three
Two girls just like their mother and a boy the image of me.
We’ll train them up in decency the way they ought to go
And I’ll ne’er forget the garden where the praties grow.

30 Responses to Where the praties grow: My seven-day potato diet experiment

  1. One of my uncles heped his farmer brother making hay during the holidays. One day he counted him eating 34 potatoes as well as other food for his lunch. Twas very hard work

  2. Picture brought back some memories. Grew up in Vancouver Island and the potatoes thrived. At one time they extended out the back of the garden extending well into the forest. I used to dig them up in the morning and cook them in various forms. One morning I pulled up a 7lb monster.

  3. Sounds like the diet Penn Jillette wrote about in his book, except he was potatoes only for a month but his initial experiences were close to yours. I think sometimes these studies that tell you how horrible a food is then later retract it are rigged…remember the bad rap butter, eggs and whole milk got for years?

  4. I think you might enjoy my brief article, “The Humble Spud,” I wrote a couple years back. Potatoes are an incredible food, in my opinion.

  5. Decades ago, in 1970s, I read that potatoes and milk made a healthy diet, so I decided to try it. Unlike you, I didn’t supplement with any fruits or veggies, just potatoes and milk, and I figured if they had milk they had cheese, so I ate that too. I was expecting that after the week I’d planned, I’d really be sick of potatoes. But I wasn’t. There are so many different ways to cook them: baked, fried, boiled, creamed, scalloped, potato soup, potato chips, etc.

    Unlike you, I didn’t get any “potato fog.” But at the time I wasn’t diabetic and I was relatively young, so maybe my metabolism converted quickly. I didn’t notice any change in my energy levels, but I’ve never been a big exerciser.

  6. There is an episode of “Freaky Eaters” about a woman who supposedly has only been eating french fries and nothing else for the last 26 years. She seems to be healthy and even has a child.

  7. I’m wondering is there a quick reference on what the potato is missing, and what foods could be added for completeness. I assume dairy is one.

    Where you said “initial adjustment period” that was kind of a revelation to me. You mean there are people out there who can get over the low-carb flu? I’ve done low-carb diets lasting up to 3 months. I lost a good amount of weight but that “flu” and “fog” remained the whole time.

  8. One serious problem I have seen with high potato consumption is fecal incontinence while exercising. The problem is typically initiated by eating a large serving of hash browns or french fries. If this is followed by walking, there is an uncontrollable urge to find a sanican, a McDonalds or in worst cases a discreet shrub within a half an hour.

    This does not always happen, but it happens often enough that I have avoid fried potatoes while out for a walk or hike. Biking doesn’t seem to pose the same problem.

    • A cow is said to poop up to 15 times and produce 30 kg manure in a single day (due to the large volume of food).

      But maybe what you´re describing is not so much a problem if water intake is restricted. There´s a lot of water in these potatoes so you won´t need to add so much more. But there could be some adjustment period for some days or weeks where a lot of material that´s been accumulated in the intestine is flushed out.

      Several years ago I tried a fruitarian type diet and had to go much to the toilet, but then often decided to eat raisins/dried fruits and honey to counteract that.

      I have been thinking recently that a high carb diet requires a lot of water, compared to a high fat diet. A camel can go for months living almost exclusively on the fat of its humps, and won´t need so much extra water. Water is liberated when the fat is metabolized.

      The composition of milk of various animals also seem to indicate this, for example you´d get 2500 kcal from just 1500 ml caribou milk (80E% fat and almost no carbohydrates), while it would take 4 liters of cow milk (30E% carbs) and 6 liters of camel or mare´s milk (60% carbs).

      So it´s possible that while a reason for all these carb related problems we have today, such as diabetes, may weel be due to a lack of nutrients found in the «paleo carbs» like fruits, vegetables and starchy roots; potassium, soluble fiber, carotenes, vitamin C, polyphenols, chlorophylls, vitamin K1 etc, it may also be due to a lack of water, so that high carb diets would be less harmful if soups are frequently consumed (as is the case in Japan).

    • The fiber content of the potatoes may be what causes my troubles…

      Potatoes are much higher in fiber per food portion than other starchy foods, such as noodles, bread and rice. 8g of fiber for 280 calories of potatoes with skin (about a pound – a healthy serving of fries, baked potato or hash browns), versus 0.5 grams of fiber for a cup of fried rice, or 1.2 grams of fiber for a cup of spaghetti. The lack of fiber may explain why the Rice Diet shows benefits for reducing IBS and fecal incontinence.


  9. Nice, I still shudder as I think back to the days I thought potatoes made us fat. I wonder if your weight remained stable as you eat a very low reward diet already and if most people would find it near impossible not to lose weight unless already lean.

  10. Interesting study about the rice diet, thanks for posting!

    The «paleo carbs» like fruits, vegetables and starchy roots (including potatoes) supplies much more soluble relative to insoluble fiber than whole grains, though. Soluble fiber seems to promote a more desirable microbiota over time. I read somewhere that the flesh of pototes have about 50/50 soluble/insoluble, while the potato skin is insoluble only. The potato skin supplies a lot of saponins and may be best avoided. Removing the skin will also reduce the fiber content.

    The bran of the grains additionally has a lot of magnesium and phosphorus/phytic acid relative to calcium, and this can also have a laxative effect. Just taking calcium carbonate (or vitamin D) can sometimes do wonders for IBS. Also a low dietary calcium/magnesium ratio has been associated with colon cancer.

    • I’ve done a little more digging on potato fiber. I think the problem comes from the microfiber. What gives a tuber its firmness and shape is an internal structure of cellules. Each of these is akin to a balloon or grocery bag, with a large empty volume and a thin but strong wall made of cellulose/pectin. Humans cannot digest these sacs.


      Not a bit of long winded exposition. One of the more unusual projects I managed in my paper research days was an attempt to make paper using sugar beets. The structure of beets is similar to potatoes. After the sugar is removed the remaining material is primarily those cellulosic sacs. These are normally ensiled and used for cattle feed. However the French growers thought they could achieve a higher value by selling them to the paper industry.

      We were supplied with about 10 tons of this ensiled stinking macerated beets in large tote bags. We shipped to Sweden and ground it up in a pilot plant, then shipped the ground material to a paper mill in Italy to use in a 10% blend with recycled fiber. It took about half a day to run it through the mill. We successfully made paper out of it, and made the paper into boxes.

      Besides the smell, the major problem with the beet paper was removing water from the pulp. The addition of the beets slowed down the paper machine by 15-20%. The mixture would not dewater properly. The beets retained an inordinate amount of water, making vacuum and pressing equiment less effective.

      The lower digestive tract is not completely dissimilar to a paper machine. If you admix a lot of microfiber – in this case thin-walled potato sacs – the efficiency of the colon to remove water is greatly reduced. If you try to force more potato through the digestive system than it can handle in the short term, well, that shrub over there suddenly looks awfully interesting….

      • Do you think that (soluble) fiber from for example fruits could be different and better than from potatoes or other roots like beets you mention?

        At least it has been shown that soluble fiber improves IBS while insoluble does not (www.ncbi.nlm.nih.gov/pubmed/26148247). In my experience, digestive problems quickly resolves if I replace grains (especially whole grains) with potatoes, fruits and honey. But there are other factors involved too, such as the fat content of the diet.

        This type of breakfast cereals like «Kellogs All-Bran with Extra fiber» supplying 26.6 grams of fiber (of which 24.7 insoluble and 1.9 grams soluble) in a one cup serving (www.prebiotin.com/prebiotin-academy/fiber-content-of-foods/), I don´t think is a great idea for anyone with IBS. Sure it could cause a bowel movement even before finishing the meal, but it may be easier to just take a Maximum Strength Laxative.

        Another interesting issue is cooked versus raw foods. In this video («Fire Starch Meat and Honey»): http://www.youtube.com/watch?v=VnN-QeMgJ_U, Richard Wrangham makes the point of the importance of fire and the cooking of foods in human evolution and how a raw type of diet (starches, raw meat, raw eggs) may reduce absorption in the small intestine by as much as 50% compared to cooked. The result is that much carbs and protein enters the large intestine where microbes will feed on it, and some of the byproducts (short chain fatty acids and micronutrients) are liberated to be used by the human body, but it is net a major caloric loss as compared to eating cooked foods. It is possible that a «benefit» from a raw food type diet is that it is in practice a calorie restricted diet. I noticed some of the fruitarians on youtube claim to eat 4000 calories per day, yet have flat bellies. But I´m not sure how much of their food is actually absorbed. One would have to eat 7-9 kg of oranges or apples to obtain this amount of calories.

        I think our small digestive system and large brains demand a calorie dense diet with cooked meat, cooked starches and honey.

        • I would ‘t say either form of fiber is better or worse, just that the colon can’t extract water fast enough to keep up when you eat a big fiber-loaded meal. Like your all bran example.

          • A difference could be that many foods rich in insoluble fibers, like whole grains, also supplies a lot of magnesium. Magnesium is a known laxative. As I´ve understood it, the way it works is by «drawing» water into the small intestine. Calcium on the other hand typically has a constipating effect. So I think the ratio of calcium to magnesium (and calcium/phosphorus) also matters, and fruits and roots have a higher Ca/Mg ratio than whole grains.

            I do however frequently consume lentils, as I find them very tasty and nutritious (esp when combined with other ingredients like fried egg, garlic, tomatoes etc). They do not give as much digestive problems, despite the very high fiber content, but they are also fairly low in magnesium with a 0.5 Ca/Mg ratio. Legumes and nuts seems to offer much more health benefits than whole grains: http://www.bmj.com/content/338/bmj.b2337

  11. Perhaps people whose ancestors adapted to this diet would handle it better and vice versa; the same way people whose ancestors domesticated cows early have less lactose intolerance. Tolerance of the diet might be assessed using continuous glucose monitoring, lipid markers, bp, exercise tolerance and such.

    • Dr. Guyenet,

      In your book, The Hungry Brain,you referenced a study where obese men lost weight easily on a bland liquid diet. When I read that, I thought, why isn’t someone bottling this stuff? Proponents of the “Potato Diet” promise fast, hunger free weight loss without the rebound effect and seems to be quite similar to a bland liquid diet. Do you think this works not only as a calorie restrictive diet but also works on the hunger and set point circuits in the brain?

      • Hi Tom,

        I do think bland, repetitive diets probably work on setpoint circuits in the brain. To some extent, people are “bottling this stuff”. There are many meal replacement shake-based weight loss programs available and they tend to be more effective than self-directed diets. The shakes aren’t necessarily bland at first but I think they get pretty tiresome after a few meals.

        My concern with that approach is it doesn’t build sustainable slimming eating habits. I think a lot of people go into a weight loss plan expecting that once they lose weight they can go back to their old habits and retain the loss, but that’s not how it works– changes have to be sustained for results to be sustained. You can’t (and probably shouldn’t) drink shakes for the rest of your life, so what happens when you stop?

        • This is the problem with almost any restrictive diet. Atkins diet does not teach you how to eat a sandwich. Shake diets don’t either.

  12. I believe the keto flu you speak of was from actually being in ketosis due to a caloric deficit in spite of subsisting on potatoes. Perhaps you increased your consumption of decreased your metabolic expenditure after those first few days and subsequently got out of that caloric deficit.

    A Richard Nikoley article puts me in mind of this theory: https://freetheanimal.com/2017/08/ketogenic-fruit-hack.html