Tag Archives: sweet potatoes

The Pearson Potato Theory of Obesity

The skeptical cardiologist developed “Pearson’s Potato Hypothesis” aka the potato theory of obesity a few years ago but became bogged down in frying oil and never published it.

Now I’m really glad I never got around to finishing my post on the theory-it appears that defenders of the potato are legion and vocal. ConscienHealth points out that a NY Times piece on the dangers of french fries quoted a Harvard epidemiologist  (Eric Rimm) as calling potatoes “starch bombs” and weapons of “dietary destruction.”

Potatoes rank near the bottom of healthful vegetables and lack the compounds and nutrients found in green leafy vegetables, he said. If you take a potato, remove its skin (where at least some nutrients are found), cut it, deep fry the pieces in oil and top it all off with salt, cheese, chili or gravy, that starch bomb can be turned into a weapon of dietary destruction.

The article goes on to recommend portion size control when dealing with French fries and further quoted Rimm:

“There aren’t a lot of people who are sending back three-quarters of an order of French fries. I think it would be nice if your meal came with a side salad and six French fries.”

Apparently the notion of limiting one’s French fries is abhorrent to many and Rimm has been attacked by thousands in the twitter-sphere.

I happen to think he’s right so I’ll go out on a limb here and post the essence of my theory without all the backing references and statistics with which I had hoped to buttress it.


Pearson Potato Theory of Obesity:

Because potatoes are cheap,  restaurants add lots of them to dishes to make the dishes seem larger and (to some) better and more satiating. Because the potatoes are so gosh darn tasty when sliced up thinly and fried and salted patrons can’t resist eating them even when they are not hungry. Eating any food when you are full is a recipe for….obesity.


To illustrate this issue I’ve started noting what restaurants serve along with the main dish that I’m interested in.

The vast majority of time breakfast orders come with fried potatoes like those below that came with the egg dish that I ordered.potato egg

I was sorely tempted to eat all these fried potatoes although full from my egg dish because when cooked properly the combination of the crispy fat, salt and warm fluffy potato interior is irresistible. Instead I ate just a few and put the rest in a to-go box, took them home, weighed them on a scale and took this picture.

IMG_8758

Interestingly, the weight of the potatoes that I had not consumed was 150 grams which is roughly equivalent to a large order of fries at McDonald’s. A large order of McDonald’s fries gives you 500 calories with 66 grams of carbohydrates,.

Thus, if I had not been disciplined that morning I likely would have ended up consuming more calories in fried potatoes than the main dish and over half of the calories I consume in a typical full day.

French fries (and their (equally addictive to me) cousin the potato chip) are the side for almost all hamburgers and sandwiches served in the US thus the possibility of unintended excess starch bomb consumption extends from breakfast to lunch to dinner in meals consumed outside the home.

Sweet Potatoes Versus Potatoes

In 2015 I pointed out that sweet potatoes which are embraced by nutrition experts are very similar nutritionally to potatoes.

A serving of either one provides 37 grams of carbohydrates and 4 grams of protein. Sweet potatoes have more fiber ( 6 grams vxs 4 grams) but more sugars (12 grams vs 2 grams.)

The Harvard School of Public health has decided potatoes are not a vegetable:

“However, potatoes don’t count as a vegetable on Harvard’s Healthy Eating Plate because they are high in carbohydrate – and in particular, the kind of carbohydrate that the body digests rapidly, causing blood sugar and insulin to surge and then dip (in scientific terms, they have a high glycemic load).”

but gives sweet potatoes a pass.

If sweet potatoes were as ubiquitous as potatoes and became a staple of fast food restaurants and a side for any and all dishes (and if they were separated out from the rest of the vegetable world), I suspect they would also be associated with weight gain.

If, on the other hand, potatoes were not markers of fast, tasty, and easily prepared and consumed food and were only eaten at trendy locavore restaurants or prepared at home, I think they would no longer be associated with obesity.

So, yes it does make sense to ask for a side salad and limit your fries to six (or perhaps seven on days of debauchery) in place of the typical mountain of potato if you are seeking weight loss.

Spudlimitingly Yours,

-ACP

Are Sweet Potatoes Healthier Than Potatoes?

In recent years, sweet potatoes have become a favored alternative to potatoes for health-conscious eaters for some reason. I’ve been noticing sweet potatoes more and more on the menus of trendy/healthy/locavore oriented restaurants as an alternative to potatoes.

A typical appraisal comes from Time’s Health magazine website:

“It’s no surprise that sweet potatoes are at the top of nearly everyone’s healthiest foods list.”

EatingWell. com proclaims,

“The sweet potato is a nutritional powerhouse. Deemed a ‘superfood’ by many nutritionists, sweet potatoes are loaded with vitamin A, vitamin C, fiber and potassium, plus phytochemicals like lutein and zeaxanthin, which promote eye health. ” (Appropriately, if you click on the nutritionists link on this quote it takes you to an Amazon.com listing of pull-up diapers!)

Please note that any article that takes the term superfood seriously should be dismissed as frivolous. Stop reading immediately and never revisit the source.

Screen Shot 2015-08-06 at 10.40.32 AMThe Cleveland Clinic website provides a comparison of the two vegetables and determines that sweet potatoes win the nutritional battle by “knock-out”. (This site also claims that sweet potatoes are far better than yams, a claim I have not had time to research)

Somehow, the idea that a sweeter, tastier vegetable is better for me than its not-so-sweet relative made no sense to me.

Call me skeptical.

Are they a healthier choice than regular potatoes or is this all driven by marketing hype?

Nutritional Differences

There are some minor differences in the nutrient content of SP and P:

Screen Shot 2015-08-06 at 8.36.39 AM
A 180 gram sweet potato has 12 grams of sugar, 6 grams of fiber and 37 grams of carbohydrate
Screen Shot 2015-08-06 at 8.35.45 AM
A 173 gram potato has 2 grams of sugar, 4 grams of fiber and 37 grams of carbohydrate

 

 

 

 

 

 

Sweet potatoes have  six times more sugar and 50% more fiber than regular potatoes. Sources that proclaim SP healthier like to focus on the large amount of Vitamin A. However, we don’t necessarily need more Vitamin A in our diet and nothing suggests these minor differences are of any importance in our overall health.

Potatoes have their own PR machine which will regale you with the wonders of spuds:

“It’s a surprise for many to discover one medium potato (5.3 oz) with the skin contains:

  • 10 percent of the daily value of B6;

  • Trace amounts of thiamine, riboflavin, folate, magnesium, phosphorous, iron, and zinc…and all this for just 110 calories and  no fat, sodium or cholesterol.

  • More potassium (620 mg) than even bananas, spinach, or broccoli;

  • 45 percent of the daily value for vitamin C

The potato people would also like you to know that:

Potatoes are a vegetable.  The popular tuber counts toward the total recommended servings of vegetables. One medium-sized potato (5.3 oz.) counts as 1 cup of starchy vegetables.

On the other hand, the Harvard School of Public health has decided potatoes are not a vegetable:

“However, potatoes don’t count as a vegetable on Harvard’s Healthy Eating Plate because they are high in carbohydrate – and in particular, the kind of carbohydrate that the body digests rapidly, causing blood sugar and insulin to surge and then dip (in scientific terms, they have a high glycemic load).”

There isn’t much good evidence that the glycemic load is something we should be focusing on with diet (see here) but the Harvard people like to point to observational studies that show that people who increased their consumption of  french fries and baked or mashed potatoes  gained more weight over time.

All observational studies try to control for confounding factors in their analysis, but in the case of food consumption it is particularly difficult because it is highly likely that those individuals who are eating french fries are also engaging in other lifestyle choices that are perceived as unhealthy.

The large observational study, which found that increased consumption of potato chips and potatoes was associated with the biggest weight gain, classifies yams or sweet potatoes as a vegetable (along with tomato juice (which is mostly sugar)and tomato sauce).  Vegetables were associated with a small loss of weight over time.

The sweet potato gets to hide amongst all the arguably really healthy vegetables (like chard and brussel sprouts and kale) that  those who are truly dedicated to a healthy lifestyle have embraced with enthusiasm.  This group also exercises optimally, avoids eating junk food and processed food, and engages in other subtle behaviors that the observational study did not measure.

Why Might Potatoes Be Associated with Obesity?

I view potatoes as a ubiquitous, cheap and quickly prepared food  that allows the rapid and easy accumulation of excess calories. The average American consumes 120 pounds of potatoes per year compared to only about 5 pounds of sweet potatoes.

French fries, a staple of fast food throughout the world, when consumed hot, combine many of the sensory elements that lead to overeating. When done properly, the frying process adds a wonderful crispness to the outside, and when combined with the warm, perfectly cooked potato on the inside, the result is irresistible.

A large order of McDonald’s french fries contains 510 calories, suddenly triple the number in a medium potato, but it only costs $2.19 and is available virtually instantaneously.

Chances are those who are consuming the McDonald’s french fries are saving further money and preparation time by combining it with a Big Mac (590 calories) and a medium Coke (210 calories). This Value Meal #1 only costs $5.69 but contains 1300 calories.

Even if you are avoiding fast food, french fries and potato chips are ubiqitous. For some reason, most restaurant breakfasts which are not pancake or waffle oriented are presented with a side of potatoes. Sandwiches always seem to come with an order of potato chips. Hamburgers are served with fries. Steaks with mashed potatoes.

For most meals that contain a potato side, up to  half of the total calories are coming from the spuds.

You have to make a concerted effort to not consume some form of potato when you are eating out, and when you do that, you are now importantly paying attention more to total calories than to macronutrient content of meals.

Your other choice is to not consume all of the french fries, potato chips, grilled potatoes or mashed potatoes that are presented as a side, but many individuals feel compelled to finish everything on their plate.

Dietary Recommendations

If sweet potatoes were as ubiquitous as potatoes and became a staple of fast food restaurants and a side for any and all dishes (and if they were separated out from the rest of vegetable world), I suspect they would also be associated with weight gain.

If, on the other hand, potatoes were not markers of fast, tasty, and easily prepared and consumed food and were only eaten at trendy locavore restaurants or prepared at home, I think they would no longer be associated with obesity.

Looking at the two on strictly nutritional or scientific grounds, it is not possible to choose one over the other.

If you are overweight and ready to lose weight, cutting out the potatoes when eating out will eliminate a lot of the carbohydrates and calories you consume. But don’t think that substituting sweet potato fries is a magical solution.

I yam what I yam,

-ACP

For a Michael Pollan video on the evil of McDonald’s french fries for other reasons take a look at: