April 2002    Vol. 1   No. 4
 

Potatoes Are Pillars of Worldwide Nutrition

Potatoes are so tied into human life and nutrition that one of the first toys to be advertised on TV and still popular after 50 years is “Mr. Potato Head.”  With its “eyes” and round body shape the potato has been used to imitate the human form.  But all fun aside, the potato has improved human health and nutrition, influenced wars, patterns of human migration, and the economy of many nations for hundreds of years. The potato is indigenous to various parts of South America; plants in a wild state have been found on the Peruvian coast, as well as on the mountainous lands of Central Chile and Argentina. The Spaniards are believed to have first brought potatoes from Quito, Ecuador to Europe in the early part of the sixteenth century.  European immigrants introduced potatoes to North America throughout the 1600s, but they were not widely grown until 1719 in America. 

According to the USDA, potatoes are the most important vegetable in the United States. Over the past several decades, frozen potato consumption rose and fresh potato consumption declined. African-Americans eat more potato chips and French fries per capita than do other Americans. Seniors favor fresh and canned potatoes, while teenagers eat more chips and French fries than do other age groups. 

The Much Maligned Potato

A recent Time magazine article put potatoes on the level of bacon grease as far as your heart and health are concerned.1 “According to Meir Stampfer, a nutrition professor at the Harvard School of Public Health, the problem is potato starch.  When you eat a potato and that starch hits the saliva in your mouth, its tightly bundled molecules immediately get turned into sugars, which make a beeline for the blood.  ‘You ate a potato,’ says Stampfer, ‘but your body is getting pure glucose.’  The flood of blood sugar sets off a chain reaction.  Insulin pours out of the pancreas.  Triglycerides shoot up.  HDL cholesterol takes a dive. ‘It's a perfect setup for heart disease and diabetes.’”  “Experts” who make these statements show telescopic vision by latching onto one small quality of a food and blowing it into national headlines – ignoring the big picture and the truth.  The focus for such statements made by Stampfer and others is a concept called the glycemic index (GI).

Glycemic Index – of Questionable Importance

The concept of glycemic index was introduced by David Jenkins in the early 1980s (He was a recent guest on my TV Show, “McDougall, MD”).  The glycemic index is a ranking based on the food’s immediate effect on blood glucose (blood sugar) levels. Carbohydrate foods that break down quickly during digestion have the highest glycemic indexes.  The value is expressed as a percent comparison with the rise that occurs with white sugar or white bread.  GI is influenced by starch structure (amylose versus amylopectin), fiber content, food processing, physical structure of the food, and other macronutrients in the meal. Low-GI foods lower glucose and insulin responses, improve lipid profiles, and increase insulin sensitivity.  Thus, some researchers believe GI has an overwhelming influence on the risk of cardiovascular disease, diabetes, and obesity. 

However, the use of GI as the sole criterion to pass judgment on a food as “good or bad” for you is wrong.  There are many other qualities of a food that contribute to its nutritional value that must be taken into consideration before recommending or condemning a particular food.   Based on GI, for example, whole wheat bread (GI=129) is worse for you than ice cream (GI = 51) and carrots (GI=131) are worse for you than sugar sweetened chocolate (GI=49). 2   A baked potato with a GI of 134 would be an unhealthier choice than a Mars candy bar at a GI of 97.   Obviously, those who condemn unprocessed high glycemic index plant foods are overlooking some serious issues. 

One of the lowest glycemic index foods is the simple sugar fructose.  The GI value is 29.  Yet this food is simply empty calories with no protein, essential fat, vitamins, minerals, or dietary fiber.  Of all the sugars, fructose is the one that raises cholesterol and triglycerides the most, and therefore would be considered one of the worst foods for people trying to prevent heart and other blood vessel diseases.3  Because of the contradictions and limitations surrounding the GI, the most recent position statement of the American Diabetic Association does not recommend using this concept in the treatment and prevention of diabetes and related complications.4 They state, “In subjects with type 2 diabetes, studies of 2–12 weeks duration comparing low glycemic index and high glycemic index diets report no consistent improvements in HbA1c, fructosamine, or insulin levels. The effects on lipids from low glycemic index diets compared with high glycemic index diets are mixed.”

Another problem with following a low GI diet is the difficulty in finding the foods and preparing the meals so they continue to be low GI foods. Food preparation, cooking, and storage will change the GI of foods.  Furthermore, it is virtually impossible to determine the GI of foods prepared outside the home. The data is conflicting and reports from different investigators reveal a sometimes-wide range of glycemic index values for certain foods.  You could spend your whole day chasing after low GI foods that in the end will not make you a speck healthier and will make you a whole lot more confused, especially when you see the negative results from all your efforts.

One of the common recommendations from “diet experts” who express concerns about the glycemic index of carbohydrate foods is for you to change to a low-carbohydrate, high-protein diet.  In last month’s issue of the McDougall Newsletter (February 2002) we discussed some of the dangers, including an increased risk of heart disease, kidney disease, and osteoporosis, of these kinds of nutritionally unbalanced diets.

Chock Full of Nutrition

Consider that the primary purpose of eating is to obtain enough energy to function throughout the day, and the body’s preferred source of this energy is carbohydrate.  Therefore, the foods that deliver the greatest amount of carbohydrate would logically be nutritionally superior and a high glycemic index food would be preferred.  So why condemn a food for doing what it is supposed to do – provide efficient fuel for your body?

There is much more to nutritionally packed potatoes than just calories.  They have 2.5 grams of dietary fiber per potato.  That translates into 50 grams for an active man and 37 grams for an active woman.  The average American eats about 10 grams of dietary fiber daily.  Ideally people on a healthy diet would eat 30 to 100 grams of fiber a day.  Potatoes are very high in vitamin C, most B vitamins, potassium and other minerals.  Just as important are the recognized health hazards you are avoiding with potatoes -- like sodium, cholesterol, and fat.  Of the calories from potatoes, only 1% comes from fat, and these few fats are mostly the kind that we need, called essential fats.

One important reason people think of potatoes as fattening and unhealthy is all the toppings poured over them, like high-fat gravies, bacon bits, cheese, sour cream, and butter.  Fortunately, there are many healthy (no-cholesterol, low-fat) toppings that you can choose like chives, salsas, low-fat tofu sour cream, low-fat soy cheeses, low-fat salad dressings, soups, chilies, marinara, and bean sauces.

Don’t confuse baked or boiled potatoes with American’s favorite forms of potatoes: French fries and potato chips.  Cooking a nutritious food like potatoes in oil increases the percentage of fat from 1% to 36% for French fries, and up to 58% for potato chips.  Often the fats used for cooking the potatoes are the most damaging forms: saturated and hydrogenated fats – linked closely with heart disease and cancer.

There is no cholesterol in a potato and insignificant amounts of cholesterol-raising saturated fats.  People in New Guinea living on diets consisting almost entirely of sweet potato tubers (with an even greater percentage of carbohydrate calories than white potatoes) and leaves have cholesterol levels on the average of 108 mg/dl.5  (Cholesterol levels below 150 mg/dl are associated with immunity from heart disease.)  Heart disease is unknown in these people on their sweet potato diet.  In animal experiments potatoes have been shown to have a particularly potent cholesterol lowering effect.6  Therefore, any expert who says potatoes will lead to heart disease ignores the scientific literature and common sense.

Complete Nutrition and Protein from Potatoes

Potatoes can provide complete nutrition for children and adults.  Many populations, for example people in rural populations of Poland and Russia at the turn of the 19th century, have lived in very good health doing extremely hard work with the white potato serving as their primary source of nutrition.

One landmark experiment carried out in 1925 on two healthy adults, a man 25 years old and a woman 28 years old, had them live on a diet primarily of white potatoes for 6 months (A few additional items of little nutritional value except for empty calories -- pure fats, a few fruits, coffee, and tea -- were supplemented in their diet).7  The report stated, “They did not tire of the uniform potato diet and there was no craving for change.”  Even though they were both physically active (especially the man) they were described as, “…in good health on a diet in which the nitrogen (protein) was practically solely derived from the potato.”

The potato is such a great source of nutrition that it can supply all of the essential protein and amino acids for young children in times of food shortage.  Eleven Peruvian children, ages 8 months to 35 months, recovering from malnutrition, were fed diets where all of the protein and 75% of the calories came from potatoes.  (Soybean-cottonseed oils and pure simple sugars, neither of which contain protein, vitamins, or minerals, provided some of the extra calories).8  Studies during the experimental feeding showed this simple diet provided all the protein and essential amino acids to meet the needs of growing and small children.

Eggs have been promoted for their "perfect pattern" of essential amino acids found in the protein.  However, when volunteer subjects were fed different foods to determine the ability of humans to utilize various protein mixtures, investigators found that our bodies can more efficiently utilize the amino acids in a mixture of potatoes and eggs -- 36% better -- than those from eggs alone.9

Potatoes Are Naturally Slimming

In our society where over-nutrition is the problem, some experts consider a high glycemic index value for a food a fundamental health hazard.  But they are mistaken – as you noticed above, the really fattening foods, like sugar, candy bars, and ice cream, are the ones with a low GI.  The potato, with a high GI, does not deserve a reputation for being fattening, because as I will show, it is virtually impossible to consume too many calories from potatoes.

One 5-ounce baked potato has 150 calories.  An active man may burn 3000 calories a day and a woman 2300 calories a day.  That means the man would have to eat 20 potatoes and the woman 15 potatoes or they would lose weight.  That’s 5 to 7 large potatoes per meal, three times a day – a big dent in even the hardiest appetite – especially considering potatoes are among the most satisfying of all foods (see below).

When it comes to the national health epidemic of obesity there are only three food issues to consider:

1)  Don’t Be Dense.  Potatoes are at the bottom of the list of calorie dense foods, at one calorie per gram.  By comparison, sugar, cheese, and beef are about 4 calories per gram and vegetable oils are 9 calories per gram.

2)     The Fat You Eat Is the Fat You Wear.  Potatoes are 1% fat – so there are virtually no fat calories to wear.  By comparison beef and cheese can be 70% fat and butter is 100% fat.

3)     Carbohydrate Satisfies the Hunger Drive.  Potatoes are at the top of the carbohydrate list with about 90% of the calories from appetite-satisfying carbohydrates.  Beef, fish, chicken, butter, and olive oil are a few examples of commonly consumed foods with no carbohydrates.  Only 2% of the calories from cheese come from carbohydrates.

One of the strongest risk factors for type II diabetes and heart disease is excess body fat.  Therefore, any expert who says potatoes will lead to diabetes or obesity is ignoring the bulk of the scientific and nutrition literature.  And they are ignoring an observation anyone can make: People living on diets high in starch (like Japanese and Chinese) are trim, young, and active people with very low rates of diabetes.

Simply Satisfying Spuds

The reason I eat is to satisfy my powerful hunger drive.  I can’t ever remember thinking about the glycemic index of my foods when I sat down to a meal.  Just fill me up and get rid of those unpleasant hunger pangs so I can get on to my next project.  In a recent experiment, 38 separate foods were fed to subjects and a rating of their level of satisfaction (satiety index) was determined every 15 minutes for 2 hours after the meal.  The highest satiety index was produced by boiled white potatoes, which was seven times higher than the lowest index of croissants. 10    Potatoes were almost 5 times more satisfying than a Mars candy bar and twice as satisfying as beef or cheese.  The main reasons for this high level of satisfaction were the low calorie density, the high carbohydrate, and low fat contents of the potato.  Carbohydrate satisfies the hunger drive, whereas fat offers almost no satisfaction.

Does It Make Sense?

People in Peru, the potato capital of the world, have about one-quarter the death rate from heart disease of  people in the USA.  Obesity and diabetes are very rare, even today, in Peru.  But things are changing.  Fast food restaurants are encroaching on Peru’s major cities -- serving French fried potatoes, shakes, and burgers.  Soon this potato-eating country will have an epidemic of diseases similar to those in the US.  Why?  Because they have abandoned their traditional foods, and especially the much maligned potato.

When you read a sensational article in newspapers or magazines, like Time, ask yourself, “Does it make sense – based upon everything else I know?”  The potato is a much loved, inexpensive, “comfort” food that continues to provide a large part of people’s nutritional needs worldwide.  And the potato should continue to make up a large part of your diet.  Based upon the facts, if famine struck and times were desperate, and I had to choose only one food to live on -- potatoes would keep me strong and healthy until the stock market’s Dow Jones Industrial Average hit 11,722.98 again.

References:

1)     Horowitz J.  10 Foods that pack a wallop.  Time January 21, 2002 pages 76-81. 

2)     Foster-Powell K.  International tables of glycemic index. Am J Clin Nutr. 1995 Oct;62(4):871S-890S. 

3)     Hallfrisch J.  Metabolic effects of dietary fructose.  FASEB J. 1990 Jun;4(9):2652-60. 

4)     Evidence-based nutrition principles and recommendations for the treatment and prevention of diabetes and related complications. Diabetes Care. 2002 Jan;25(1):202-12. 

5)     Luyken R. Nutrition studies in New Guinea.  Am J Clin Nutr 14:13-27, 1964. 

6)     Morita T. Cholesterol-lowering effects of soybean, potato and rice proteins depend on their low methionine contents in rats fed a cholesterol-free purified diet. J Nutr. 1997 Mar;127(3):470-7. 

7)     Kon S.  XXXV.  The value of whole potato in human nutrition.  Biochemical J 22:258-260, 1928. 

8)     Lopez de Romana G.  Fasting and postprandial plasma free amino acids of infants and children consuming exclusively potato protein. J Nutr. 1981 Oct;111(10):1766-71. 

9)     Kofranyi E.  The minimum protein requirement of humans.  Tested with mixtures of whole eggs plus potato and maize plus beans.  Z. Physiol Chem 351 1485-1493, 1970. 

10) Holt S.  A satiety index of common foods.  Eur J Clin Nutr. 1995 Sep;49(9):675-90.

 

2002 John McDougall All Rights Reserved


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