Potatoes and Human Health, Part II

Glycoalkaloids in Commonly Eaten Potatoes

Like many edible plants, potatoes contain substances designed to protect them from marauding creatures. The main two substances we're concerned with are alpha-solanine and alpha-chaconine, because they are the most toxic and abundant. Here is a graph of the combined concentration of these two glycoalkaloids in common potato varieties (1):

We can immediately determine three things from this graph:

• Different varieties contain different amounts of glycoalkaloids.
• Common commercial varieties such as russet and white potatoes are low in glycoalkaloids. This is no accident. The glycoalkaloid content of potatoes is monitored in the US.
  
• Most of the glycoalkaloid content is in the skin (within 1 mm of the surface). That way, predators have to eat through poison to get to the flesh. Fortunately, humans have peelers.

I'll jump the gun and tell you that the generally accepted safe level of potato glycoalkaloids is 200 mcg/g fresh weight (1). You can see that all but one variety are well below this level when peeled. Personally, I've never seen the Snowden variety in the store or at the farmer's market. It appears to be used mostly for potato chips.

Glycoalkaloid Toxicity in Animals

Potato glycoalkaloids are undoubtedly toxic at high doses. They have caused many harmful effects in animals and humans, including (1, 2):

• Death (humans and animals)
  
• Weight loss, diarrhea (humans and animals)
  
• Anemia (rabbits)
• Liver damage (rats)
  
• Lower birth weight (mice)
  
• Birth defects (in animals injected with glycoalkaloids)
  
• Increased intestinal permeability (mice)

However, it's important to remember the old saying "the dose makes the poison". The human body is designed to handle a certain amount of plant toxins with no ill effects. Virtually every plant food, and a few animal foods, contains some kind of toxic substance. We're constantly bombarded by gamma rays, ultra violet rays, bacterial toxins, free radicals, and many other potentially harmful substances. In excess, they can be deadly, but we are adapted to dealing with small amounts of them, and the right dose can even be beneficial in some cases.

All of the studies I mentioned above, except one, involved doses of glycoalkaloids that exceed what one could get from eating typical potatoes. They used green or blemished potatoes, isolated potato skins, potato sprouts or isolated glycoalkaloids (more on this later). The single exception is the last study, showing that normal doses of glycoalkaloids can aggravate inflammatory bowel disease in transgenic mice that are genetically predisposed to it (3)*.

What happens when you feed normal animals normal potatoes? Not much. Many studies have shown that they suffer no ill effects whatsoever, even at high intakes (1, 2). This has been shown in primates as well (4, 5, 6). In fact, potato-based diets appear to be generally superior to grain-based diets in animal feed. As early as 1938, Dr. Edward Mellanby showed that grains, but not potatoes, aggravate vitamin A deficiency in rats and dogs (7). This followed his research showing that whole grains, but not potatoes, aggravate vitamin D deficiency due to their high phytic acid content (Mellanby. Nutrition and Disease. 1934). Potatoes were also a prominent part of Mellanby's highly effective tooth decay reversal studies in humans, published in the British Medical Journal in 1932 (8, 9).

Potatoes partially protect rats against the harmful effects of excessive cholesterol feeding, when compared to wheat starch-based feed (10). Potato feeding leads to a better lipid profile and intestinal short-chain fatty acid production than wheat starch or sugar in rats (11). I wasn't able to find a single study showing any adverse effect of normal potato feeding in any normal animal. That's despite reading two long review articles on potato glycoalkaloids and specifically searching PubMed for studies showing a harmful effect. If you know of one, please post it in the comments section.

In the next post, I'll write about the effects of potatoes in the human diet, including data on the health of traditional potato-eating cultures... and a curious experiment by the Washington State Potato Commission that will begin on October 1.


*Interleukin-10 knockout mice. IL-10 is a cytokine involved in the resolution of inflammation and these mice develop inflammatory bowel disease (regardless of diet) due to a reduced capacity to resolve inflammation.

How to get invited to give talks

It's good to give talks at other institutions as a graduate student. You get to meet new people, learn about new research areas, swap ideas, get feedback on your work, get practice giving talks, etc. And it looks nice on your CV.

As far as I can tell, there are about four ways to get invited to give talks:

Photo by Husky

1) Be a superstar, and people will just invite you to give talks all the time

This is pretty unlikely as a graduate student, unless you're like my friend Hedy, who seems to get talk invitations all the time. She also is often asked to serve on program committees, submit journal papers, etc. Her research is just that smoking.

2) Have an advisor who is good at networking

I'm sorry to say odds are stacked against you if you're a Computer Scientist, because we all know how the joke goes: "The introverted Computer Scientist looks at their own shoes while talking, and the extroverted Computer Scientist looks at yours." Lots of truth there.

Some people get lucky, and if they don't get advisors who are good at networking they at least get ones who are superstar researchers. What happens in this case is the superstar advisor is so busy being awesome they have no time to accept all the invitations they get, thus passing them on to you.

For those of us who are (not yet) superstars, and/or have shy advisors, how do you get talk invitations? Well, I've found two tricks to work pretty well -

3) Talk swap

The idea here is you know someone who is doing neat research, and they either live close to your institution or they will be visiting some time soon. So you invite them to come give a talk. Often times, they will return the invitation. A colleague and I did this once recently. His institution is an hour away from me. So he gave a talk in my research group, and a few weeks later I traveled to give a talk at his research group.

4) Invite yourself

Academics, at least Computer Scientists, love to be entertained. So when we have someone who says, "Hi, I'm doing research in area X. I'm going to be in town the last week of November, can I come give a talk?" most places are very happy to have you. Especially if you come on someone else's dime. I've never done this cold - I've always at least known someone who knew someone - but I know people who have and I think it's perfectly acceptable.

You can do this if you're traveling for academic reasons (e.g., conference, project meeting), but you can also do it when you're going somewhere for a vacation. Though do keep in mind you're more likely to receive a "yes" if you offer to come during the fall or spring semester. Winter break and summer are usually not the best time to go give talks, at least at my university, because many people are away.

If you are shy yourself, it can be a bit nerve wracking to invite yourself somewhere, but it's worth doing. The worst that happens is someone will say "No thank you," but it's really a small risk and can pay off handsomely. I've made a lot of fantastic contacts and met quite a few collaborators due to giving talks at their institutions, and learned about new areas of research which later fed into my own work.