On Personal Insight

by Hayden-William September 27, 2026

Time to Read: ~9 Minutes

From the Archives: This is an original (pre-2021) SFF blog post that has been reposted with updated information.

Take Home Points:

It is important to give extra emphasis to well-conducted, published scientific studies when trying to decide what factors are important to human health.
However, this mindset has made some people discard personal observations and anecdotal information.
Although not ranked as high on the evidence hierarchy pyramid, personal observations and anecdotes should be considered.
My observation that my adult lactose intolerance seemed not to apply when I ate cold pizza was a personal observation that served me well and enabled me to eat my favorite food as an adult.
Years later, evidence became available that demonstrated my personal observation was grounded in truth.

Introduction

Here at SFF we often speak about the importance of critically and objectively evaluating published scientific studies when deciding what information is appropriate to apply to your own health and fitness. This is a response to the all-too-common misrepresentation (or dismissal) of scientific studies by the media. However, does this mean that we should ignore unpublished observations, anecdotes and opinions that we or others may have? Although it may seem counterintuitive, we actually should be considering them if we take the process of scientific inquiry seriously. Remember that scientists aim to be as objective as humanly possible and part of this means considering all the evidence. Although unpublished observations, anecdotes and opinions do not constitute strong evidence, they are still a form of evidence and therefore included at the base of the evidence hierarchy pyramid. Sometimes this evidence turns out to be baseless, but there are times where it may hold a seed of truth. To illustrate this point, I will give an example from my life.

Lactose Intolerance

When I was younger I, like many children, consumed a lot of dairy products. I loved cheese, ice cream, pizza, etc. The list went on. Dairy products such as these are made with milk and unlike most carbohydrate- (sugar) containing foods, the sugar in milk is lactose. Lactose is a disaccharide, which means it is two sugar molecules (galactose and glucose) bonded together.

Structure of lactose (From Science In School)

In order to break down ingested lactose we must do so using an enzyme (enzymes are specialized proteins) called lactase which is secreted by our small intestine. Unfortunately, as humans get older, production of this enzyme often decreases, which means that more of the ingested lactose will pass through our small intestine without getting broken down. When undigested lactose reaches our large intestine, the bacteria that reside there have a field day breaking it down for us. They do so in a manner (fermentation) that produces a great deal of gas (carbon dioxide, hydrogen, and methane), which then causes various unseemly abdominal conditions. This "lactose intolerance" is actually quite common. Around 25% of the U.S. population suffers from the condition and a larger percentage likely experiences some aspects of the condition to a more manageable degree. Indeed, surveys of various mammals during and after weaning suggest that the norm is actually to lose the ability to produce lactase and that those individuals who can digest lactose easily as adults are not the norm, and thus, quite lucky.

A Chance Observation

As I got older and finished out college, I developed the classic symptoms of lactose intolerance. I had a very hard time digesting dairy products without side-effects. Ice cream and cheesecake were now catastrophic consumables as were thick cheese sauces like Alfredo sauce. Of course, there were over the counter lactase pills and I tried them, but they never seemed to work. In a fit of rage I even took an entire bottle of lactase pills with just one spoonful of ice cream. It didn’t work. I realized then that I would have to shift my diet and exclude dairy foods. However, pizza was (and still is) my all-time favorite food. I was unwilling to give this up. But of course, a piping hot slice of pizza was enough to do me in. I had resigned myself to just having to bite the bullet now and then when I wanted pizza.

One day I ate leftover pizza when I was too lazy to heat it up. This cold pizza didn’t bother me at all. I ate another piece and still there was no effect. I was baffled. Being a budding scientist, I then conducted some mini-experiments trying different types of pizza and eating slices at different temperatures. The end result was that as long as the pizza was room temperature or colder, I would experience minimal to nonexistent symptoms of lactose intolerance. Such a result made no sense to me as I still could not eat other cold dairy products like ice cream or milk. But pizza was fine. It appeared to be a phenomenon unique to dairy in the form of cheese. I was ecstatic and whenever I encountered someone who was also lactose intolerant I would let them know of my “finding” and suggest they try it. There was much initial skepticism from those who heard my claims. The response was usually something along the lines of, “I’ve never heard anything like that before” or “But that doesn’t make any sense based on what causes the symptoms” These reactions were perfectly natural and reasonable. At the time, there was nothing out there to support my claims.

A Mechanism For The Observation?

Years later, scientists would conduct a study that would give some credence to my claim. A study by Peuhkuri et al., 2000 (PMID: 10757456) examined the severity of abdominal symptoms caused by lactose solutions of different temperatures. They found that the cooler solutions resulted in fewer disagreeable symptoms. Ah ha! Unfortunately, the study didn’t go any further than that. Why this phenomenon might affect lactose in my pizza cheese and not lactose in my ice cream was not explained by the study.

However, since the original writing of this article several studies have been published that given a likely explanation to my "cold pizza" effect. A study in 2009 by Bhattacharya and coauthors found that warm liquids/meals with lactose are digested (pass through the stomach) much quicker than cold ones. Thus the amount of lactose reaching the fermenting bacteria will be much greater at any given time in a hot pizza. This will result is a lot of fermentation products (gas) occurring at one time. Another key piece of information comes from a 2023 article by Atik & Huppertz where they note that when cheese melts, the fats are separated from their bound carbohydrates. Therefore if pizza is eaten hot, the fat portion of cheese separates from the carbohydrate portion. The issue here is that the fats move through your digestive system much faster when they are melted and separated like this. Thus the now freed lactose has another force pushing it through your digestive system at a more rapid pace.

Taken together the above data explain try "cold pizza" phenomenon. Because cold, solid, fatty foods move through your digestive system slowly, a cold piece of pizza will see its lactose reach the large intestine bacteria much slower, giving time for the symptoms (gas) to be spread out and handled more manageably. By contrast, piping hot pizza with its warm temperature and separated fat will rush through the digestive system much more quickly. The same concepts here can be applied to ice cream. As you eat ice cream it becomes liquid and although it is cold, the liquid nature of the food makes it pass through your system very quickly which leads to intense lactose intolerance symptoms.

Final Thoughts

When I first encountered my "cold pizza" phenomenon I didn't really have good evidence to support what I was seeing (that I could eat cold pizza with no problem, but not hot pizza). Given that I didn't have a wealth of strong evidence, should I have ignored my personal observations? I think we can all agree that my observations were good and there was no downside to believing them. Indeed there were only upsides - being able to eat my favorite food. Of course, anyone can give their personal insight on just about any topic and far too many people seem to do just that on social media these days. Unfortunately, this is a big reason why scientific discoveries or announcements wind up being wildly mis- or over-interpreted.

So, what is one to do? I can give no hard and fast rule here. Ultimately it comes down to trust. Do you trust the opinion of the person or organization who is giving you their “insight”? Physicians have a lot of personal insight as they see many different patients and may see rare cases. They may feel this experience is enough to give a recommendation to you or other patients without a lot of strong evidence. Personal trainers, massage therapists, physical therapists, and even PhDs can have great insight on matters that they may not have been able to publish.

In the end, remember that everyone is human and that not everything observed may apply to every individual. And of course, many experts also have biases. So, you will have to make your own judgement as to how credible you feel a particular piece of personal insight is likely to be. There is some great insight to be gained from others and as such I will continue to share my insight when appropriate. When I do, though, take it for what it is by remembering a quote by Mr. Bruce Lee:

“Absorb what is useful, discard what is useless, and add what is uniquely your own.”