Thursday, May 31, 2012

The Paleo Diet: Follow-Up IV

According to Dr. Ravi Bhatia, a doctor who specializes in leukemia, you shouldn't experiment on yourself, because "you won't learn from it, and others won't learn from it, either." While this view is almost certainly too strongly worded, there are many ways self-experimentation can go wrong. Besides being potentially dangerous, it is far too easy to fall prey to myriad cognitive biases. Of course, scientists, working in their labs, face all of these same issues, but perhaps not to the same extent. After all, it is common wisdom that it is much easier to be objective about others than ourselves.

In order to combat the pitfalls specific to self-experimentation, it helps to have multiple sources of independently collected data. As I mentioned before, United Blood Services records several pieces of information about each and every person that chooses to donate blood and provides that information to donors via their official website. Luckily, I donated blood both before and after starting my Paleo Diet experiment, so I do have some data in which to check against that collected by myself on at least several different dimensions.

I started the experiment almost immediately after my blood donation on 10/12/2011, so this graph represents 6 independently collected datapoints of my total cholesterol (5 before starting the experiment and 1 after). For some reason that escapes me, my donation on 7/23/2010 only has data for total cholesterol and not any other of the measures. Even simply eyeballing the graph, it is quite clear that my total cholesterol has risen since I started eating Paleo. The mean pre-experiment total cholesterol is 154 mg/dL, which is a full 47 mg/dL lower than the datapoint from after I started the experiment. WebMD tells me that my pre-experiment total cholesterol is "desirable", but that my during-experiment level is "mildly high". On the other hand, my total cholesterol level is only in the "mildly high" category by 1 mg/dL which is probably within the margin of error. In any case, I think it is (moderately) safe to conclude that adopting a Paleo Diet has caused my total cholesterol to increase (but not dangerously so).
Based on the 3rd-party data, my blood pressure hasn't seemed to change much since I started the experiment. The pre-experiment mean for my systolic blood pressure was 115 mmHg and my during-experiment datapoint was 118 mmHg. The difference is well within the margin of error. My previous diastolic blood pressure had a mean of 65 mmHg while my latest datapoint was 75 mmHg. I'm not really sure if this falls within the margin of error, but I regularly observe about that much variance between two consecutive days according to the data I have been collecting on my own. A possible confounding factor with the particular set of data is that on the pre-experiment days I donated blood shortly after waking up, while the latest datapoint was just before I went to bed (due to shift changes at work). I'm not sure how large of an effect (if any) this has had on the data, but either way, I don't think my blood pressure has changed much because of my diet.

My mean pulse pre-experiment was 65 BPM and my during-experiment datapoint was 53 BPM. While lower numbers are usually considered to be healthier, numbers lower than 60 BPM are considered to be a condition called bradycardia. WebMB advises me that without the presence of negative symptoms like light-headedness or chest pain, "a slow heart rate is sometimes normal and can be a sign of being very fit" and that "healthy young adults and athletes often have heart rates of less than 60 BPM". This doesn't seem to be much cause for concern and is weak evidence that my physical fitness has improved.
Hemoglobin levels are something that United Blood Services records, but that I don't. Judging from the graph, it appears that my hemoglobin levels had been increasing over time and then reversed after starting the experiment. I basically have no idea what this means or if this is even enough data to be meaningful. If anyone knows how to interpret this information I would very much like to hear it.


Body temperature is another measure I haven't been recording, but that UBS has. I was slightly colder during my last visit than on previous occasions. The mean pre-experiment temperature was 98.4 degrees Fahrenheit, but my most recent datapoint was 97.3 degrees Fahrenheit. I suspect this is another one that has been confounded by me switching the time of day of my visits. On the other hand, I think I would have predicted an increase in temperature and not a decrease, because only for the last datapoint was I completely "warmed up" by going about an entire workday before donating blood. I'm not sure what to make of this. Any ideas?
According to the graph of the UBS data, my BMI was slowly increasing and then dropped off significantly. My pre-experiment BMI came out to a mean of 25.9, but my latest datapoint put me at 21.6.

Overall, the data collected by UBS seems to roughly line-up with the data I collected myself. This increases my confidence that the relationships I have been observing in my data aren't merely artifacts and that I'm probably not too hopelessly biased to use the results I get from self-experimentation for important life-style choices.

5 comments:

  1. I've heard that high cholesterol—i.e., higher than what most nutritionists recommend—is good, at least for men. But I have absolutely no context for that claim, so take it with a big dose of cholesterol.

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    Replies
    1. Yeah, among the Paleo Advocates, this is more or less the standard view.

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  2. I think your body temp lowered bc of your weight loss. Less heat insulation? either way, it didn't lower much. It could've been nothing.

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    Replies
    1. Yeah, you are probably right that it is simply due to randomness. Another possible explanation is that the AC was turned up higher that day.

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