Friday, September 23, 2011

Potatoes and Protein

The Food and Nutrition Board of the National Academies of Science publishes the Dietary Reference intakes, which includes Estimated Average Requirements for Indispensible Amino Acids for Adults Aged 19 years or Older.

I decided to find out whether the average person could meet his or her IAA requirements eating a diet composed solely of white potatoes.  I used the USDA nutrient database to find the amino acid delivery of potatoes at 1880 kcal and 2350 kcal, approximate caloric requirements of a 120 pound woman or a 160 pound man, respectively.  I created the following table for the purpose:
Click for larger version

According to these FNB and USDA data, the average person can meet all indispensable amino acid requirements eating potatoes as his/her sole protein source.   No 'limiting amino acids' nor protein complementing required so long as caloric requirements are met.

Kon and Klein reported in 1927 on The Value of Whole Potato in Human Nutrition.  Two healthy adults obtained all of their protein and IAAs from potatoes for 167 days.  They maintained nitrogen balance.  They reported:

"The digestion was excellent throughout the experiment and both subjects felt very well. They did not tire of the uniform potato diet and there was no craving for change."

The potato provides only about 10% of calories as protein.  A mixed diet containing other plant foods providing higher proportions of protein, like green vegetables (20-40% of calories as protein), nuts (~25% of calories as protein), or legumes (~25% of calories as protein) will provide higher levels of the IAAs and total protein.

It seems that humans can obtain all of the protein they require from a food like the potato.  What does this tell us about ancestral nutrition?   

I decided to compare the IAA delivery of potatoes to that of 95% lean ground beef.  I compared the IAA delivery of amounts of beef and potatoes that provide comparable total protein, and created the following table to illustrate:
Click for larger version
Both the beef and the potato provide adequate amounts of total protein and IAAs. The much smaller portion of beef (200 g vs 2500 for the potatoes) provides larger doses of the IAAs, presumably constituting greater excesses of IAAs for the average individual.

The body will deaminate and oxidize these excesses of IAAs, increasing the amount of ammonia the liver must detoxify and sulfuric acid and urea the kidneys must excrete.

Since the beef supplies only about 14% of total energy requirements, the individual who fills in the other 86% of calories with whole foods that also provide protein will automatically consume a higher amount of IAAs than one who consumes a mix of plant foods with a far smaller amount of animal protein.

For those who have concerns about overconsuming methionine because some research suggests that reduced methionine consumption might increase longevity, I find it interesting to note that the ground beef provides about 15 times more methionine+cysteine per unit weight than the potatoes (about 9.5 mg per g cooked beef, versus 0.6 mg per g cooked potatoes).  

Let's say someone consumes the half-pound of beef (328 kcal) and gets the remainder of his required 2350 calories from potatoes (2022).  He would get 1906 + 0.86(1425) = 3132 mg of methionine+cysteine, compared to 1425 mg (less than half as much) if he ate only potatoes. 

I wonder if the body has an internal regulatory mechanism for amino acid consumption, which drives appetite to control total amino acid intake, such that if a person eats a diet rich in animal protein, the sytem drives the appetite toward attempting to fill the bulk of caloric requirements with low protein items like fat/oil, sugar, fruits, some very low protein tubers (e.g. cassava), or some refined starches?


Chris Sturdy said...

Pretty impressive for the much maligned potato! Interesting stuff, Don!

Jack Christopher said...

Curious on your thoughts about increased protein need during dieting/to help main lean mass on a defecit?

I have no citation for that but I think Casey Butt, Lyle McDonald or Martin Berkhan do.

Edo Ergo Sum said...

I have some many questions...
They both lost weight, but I would like to see how the body composition change over this period of experiment. What about anti-nutrients in potatoes? How can we know that nitrogen ingested was absorbed and excreted? Maybe N excreted was from muscle protein breakdown? They were consuming potatoes unpeeled, how fibre would effect absorption of proteins?
Also this research was done under direction of Funk who discover vitamins. I think it was the time(1920's) of new discoveries and everyone was looking for more new discoveries. I wouldn't be surprised if they were trying to find something "magic" in potatoes. In this research they are talking about vitamin deficiency diseases like beri-beri and pellagra but those disease are caused be fungal infection(supplementation of vitamin B didn't cure the people)?

Peter said...

The potato man kept his diet only on potato for 60 days, high-carb diet: here's the digits,

Beginning weight: 197
Beginning blood glucose: 104
Beginning cholesterol: 214
Beginning triglycerides: 135

60 day weight: 176
60 day blood glucose: 94
60 day cholesterol: 147
60 day triglycerides: 75

Blood pressure from 122 to 70

Yes, Don, what's your intake on the controversial idea that muscular activity increases the need for extra dietary protein (apart from the overall need for increased calory intake)

malpaz said...

can you do a post on iron, and iron overload in relation to health and the other vitamins/minerals necessary to keep the iron levels hormetic. i think i have some major iron overload problems in my body. giving blood thursday and wondering what kind of blood work would be necessary to at least prove my point to the doctor

Jim Purdy said...

Don, I wouldn't expect you to spend time on researching this question, but I wonder if you think that a diet based on tomatoes might work much better than potatoes?

I have been experimenting with something close to a tomato mono-diet, and it seems to be helping with my obesity, type 2 diabetes, hypertension, lymphedema, and more.

That doesn't surprise me, because tomatoes co-evolved with animals, offering good nutrition to the animals that eat and later disperse their seeds.

Potatoes, on the other hand, would have no evolutionary benefit in being eaten by predators, so I would expect tomatoes to be much more healthful than potatoes.

montediaz said...

I second that. I've been wondering about iron overload as well Don. It seems like a "paleo" lifestyle may promote this condition.

Don said...




The RDIs for protein and IAAs are calculated to cover the needs of 98% of the population, and include a large safety factor. In fact, most people need less protein than these figures suggest. When dieting, the most important thing is to spare protein from being converted to carbohydrate; the best way to do that is to ensure adequate carbohdyrate intake. And for maintaining lean mass, the most important thing is to engage in high intensity exercise. Studies with animals have shown that if exercise is of high enough intensity, the body will maintain lean mass even during starvation, stealing protein from other tissues to maintain it.

Don said...


I think that for probably half of the population, eating the RDA for protein already provides all the protein required to satisfy needs generated by high intensity muscle activity. I should do a post on this. If you run the numbers, if you were gaining a pound of muscle per week, you would need 20 g of extra protein per day, easily achieved by varied diet, even without animal food...but most people are NOT gaining a pound of muscle per week.

Brad Pilon's book How Much Protein (link in my right side bar) reviews the research on this topic, and it shows that most people need no more than 70 g of protein daily to build muscle at typical rates. You can easily achieve this with a varied diet with no emphasis on "high protein" foods.

Don said...


If you can eat enough tomatoes to meet your caloric needs, I am sure the tomato-based diet supplies a better overall nutrient profile. Tomatoes provide about 22% of calories as protein, whereas potatoes only about 10% of calories are protein. Trouble is, you would have to eat 10 kg/22 pounds of tomatoes daily to get 1800 kcal. I might do all the calculations to see how they supply IAAs, but I am sure they would cover them. If you could eat enough.

Don said...

Malpaz and Montediaz,

Iron post is up.

Obi said...

This is amazing, I have been vegan for 2 years now and have found it such a pain worrying about my protein intake. Seeds give me stomach pains, pulses make me bloated, and soya messes with my hormones. Only 4 days ago I decided to try and meet my calorie/protein requirements with potatoes and almonds as my main source, I find it easy to eat 500g of potatoes in one meal and that's over 10g of protein, My target is 30g of protein a day, as I don't buy into the 0.8g per kilo of body weight, thats propaganda and the over safety guidelines its more like 0.3 g per kilo for optimum results and I don't weigh much.

I find this information fascinating. I am very happy because I know that from experience potatoes are SO easy to digest and they leave me feeling very satisfied and energized. Thank you for taking the time to write this up. :)