Answering Nutrition Questions
People consistently write me with new nutrition questions. Sometimes I can quickly answer the question. Other times, it would take a lot of research, and I am unable to answer. Often, the question is in response to an article they've read on the Internet or in a magazine saying something that contradicted what they thought was true.
It seems like half the questions I get are about something someone has read about soy. If you have a question about soy, please see the articles on soy on the VeganHealth.org site.
Because I get so many questions, I'd like to shed some light on nutrition and how to find out what is known about your particular question.
I get the impression that many people imagine that there is an existing body of all knowledge about nutrition, and some people have access to this body of knowledge. The truth is that a great deal about nutrition is simply not known. In fact, I can easily sit here and come up with a very long list of questions for which there are as of yet no answers. If someone says they know the answer, they are either kidding their audience or themselves.
When I hear someone state a surprising nutritional fact, I ask myself a number of questions:
- Does this sound too good to be true? If it does, it probably is.
- Does this sound too bad to be true? If it does, it probably is.
- How does the person saying this know it to be true?
Answering question #3 can save a lot of time. People often just read a popular article or book and then start stating something as though they know it to be true. The information might have been based on test-tube studies (virtually useless for applying to everyday behavior), animal studies (ditto), their own personal experience with their patients (a highly self-selected sample with a lot of bias), or on a handed down tradition. Given the immense number of nutritional factoids and theories making the rounds these days, none of the above forms of knowledge provide enough evidence for me to worry about a potential problem or change my behavior (unless I'm having a problem and have nothing to lose).
Self-selection is when those in the group being studied become part of the study group because they have responded well to treatment. For example, a doctor may put patients on program X. Those who don't respond to program X stop seeing the doctor and the remaining patients end up with a high positive response rate. If you only look at the patients who finished treatment, you have a highly self-selected sample and the results will not correlate well to the overall population.
I take some comfort from the fact that, although so much is unknown about nutrition, what is not known has little chance of harming me. Yes, a diet that is terrible on many fronts could make me chronically ill, especially if I didn't exercise regularly. But eating 4 servings of soy a day versus 3, 2, 1 or 0 just isn't going to affect my long term health in any predictable way.
There are people with specific illnesses that have a strong nutrition component, such as celiac disease (severe gluten autoimmune disorder). Also, elevated homocysteine (from a lack of B12, folate, or vitamin B6), or lack of omega-3s may lead to stroke, heart disease, and dementia in many people. So there are important nutritional considerations, but they make their way to the public as evidence is discovered.
I encourage all vegans to read the article Staying Healthy on Plant-Based Diets to make sure you are getting the nutrition that we know to be important and avoiding that which is known to be particularly harmful.
For optimal health, everyone's diet should include whole plant foods - fruits, vegetables, whole grains, beans, and nuts. Exercise is important for preventing type 2 diabetes and many other diseases.
More and more, in an attempt to adjust for the myriad of biases and confounding factors, nutrition research is becoming statistics-intensive. Meta-analysis in particular are almost completely about statistical methods. There is good reason for this, but I sometimes have to wonder that if a result isn't strong enough to be obvious after just basic adjustments (e.g., a study on lung cancer and vegetables should adjust for smoking, caloric intake, etc.), then is it really all that important? I suppose debates like this will eventually take place and be settled.
That is my general nutrition sermon. Still, people have legitimate questions, some of which might have answers.
Finding Information
An obvious way to look for information is to go on the Internet and do a search. However, this can lead to a lot of misinformation. One way to get an idea of what kind of information you are getting is to look at the references (if there aren't any, it's a good reason to be skeptical). If the references appear to be mostly test tube or animal studies, I'd continue to be skeptical.
A more tedious but more effective way to answer questions is to do a search on PubMed.
Plugging words into the "for" bar and hitting "go" will give a list of papers (in most cases, peer reviewed) which contain those words. You can then click on the study to see if there is an abstract. You can also click on "Related Articles" to find other papers on the same or related subjects.
Some quick hints:
- You can search for a phrase by putting it in quotation marks.
- You can search for multiple variations of words by beginning or ending them with an asterisk. For example, if you want to search for "vegetarian or vegetarians," you can enter, "vegetarian*" and it will search for any word beginning with "vegetarian."
- Words can be linked with "AND" or "OR." You can search for all studies having to do with vegan or vegetarian diets by entering: vegan* OR vegetarian*
- If you click on "Limits" it will take you to a page which gives many choices, such as stating that you are only looking for human studies. Caution: It doesn't always successfully follow the chosen parameters.
- If you read an article and are interested in seeing an abstract of a cited paper, you can often find it by going to PubMed and clicking on Single Citation Manager in the left-hand sidebar. I usually enter only the year (in "Date"), the volume, and page and the article will be listed in the results.
- Sometimes you can find an abstract even more quickly by simply cutting and pasting a citation into the search bar at Google.com.
Be aware that initial searches will sometimes provide an abstract or two saying one thing, but that you often will find much different results by digging further. If I am trying to do a thorough job on a topic, I try to look up the most recent review of the topic, get a copy of the review (sometimes available free on line, but more often from a local public university library) and see the articles cited in the review.
The jargon used in many abstracts can be difficult. I, too, am often unfamiliar with some of it. Each area of research has their own terms and you just have to do the best you can in interpreting what's said. Since I'm not interested in an area until studies are performed with actual humans, I have to deal mostly with statistics jargon (usually accomplished by assuming they knew what they were doing) and less with biochemistry.
I hope the above can help anyone with nutrition questions find out what research has been done and what the general results have been.