Written by Kara Collier
There is no such thing as a one size fits all diet, we are all unique individuals with unique responses to the foods we eat.
Your baseline genetics influence your diet and may predispose you to a variety of health outcomes.
The quality and diversity of your gut microbiome plays an important role in overall health.
If you spend much time reading about health or nutrition, you know that there is a lot of contradictory information out there. Your doctor may be trying to convince you to eliminate animal products in order to reduce your risk of heart disease, the latest health-book craze may be all about substituting vegetables with butter and steak, and your friend keeps telling you that going vegan changed their life! Making sense of all this information can be overwhelming, and the question of 'who is right' never seems to be resolved. Just like that, we keep looking for the next best thing and never quite knowing if we've found it.
This large amount of conflicting information has to do with how difficult (some say impossible) it is to run a long term study which determines how diet affects health outcomes. Imagine having to monitor participants for multiple decades, trying to standardize what they eat, their exercise routine, and any other external factors which may affect their health or longevity. We would essentially need to turn people into lab mice in order to achieve anywhere close to this level of control!
So does this mean we should ignore nutrition and health research altogether? Of course not, it simply means that we may be limited to observational or epidemiological studies when it comes to answering certain types of questions. These types of studies are usually based on survey data and other imperfect sources of information. They are also prone to many sources of bias, meaning that their conclusions often have to be taken with a large grain of salt. Finally, if the Ph.D. scientists who develop these studies fall into the traps of statistical bias and make incorrect conclusions, imagine how much the mass media (and folks like us) get wrong. We can't all be statisticians after all!
Now, imagine a world where we have the resources, people, money, and ethics necessary to conduct the perfect, controlled research study on human beings. They spend decades living in a meticulously controlled environment, where every aspect of their life is observed and documented. We should expect to finally be able to answer the question, 'which diet is the best' right? Unfortunately, the answer is no. Mouse and animal experiments do exactly this, but can still end up with contradictory results for many reasons (including the genetic diversity of the animals). We are all different enough from one another that the idea of a one size fits all diet is most likely just a pipe dream.
For example – a recent study showed that 90% of participants experienced a major blood glucose spike after consuming a bowl of corn flakes and milk. These same participants had highly variable responses to other foods such as bananas, rice, yogurt, etc. Their difference in blood glucose response for the other foods was 44 ± 31 mg/dl. What can we glean from results like this? It's pretty likely that eating corn flakes every day is not good for the majority of us, however, it doesn't say much about the foods which show a large variability across participants. You may have a 50/50 chance of responding well to bananas for example. This just goes to show how different we are, not just in our glucose responses, but many other health parameters as well.
What has been proven pretty decisively is that pretty much all diets are better for health outcomes than the Standard American Diet (or SAD for short; very appropriately titled). This diet is high in processed carbohydrates, sugars, refined oils, processed meats, and contains little fiber and vegetables. But as they say, the devil is in the details. Expecting any diet to fit your needs perfectly is overly simplistic. We want to help you figure out the nuances and uncover the optimal diet for you!
Our genes make us all unique (even identical twins have differences in their DNA!). One example of a gene that affects our dietary choices is the APOE gene. It codes for a very important protein involved in fat metabolism. There are a few common variants of this gene, and the E4 variant is associated with an increased risk of cardiovascular disease, Alzheimer’s disease, and a higher sensitivity to saturated fat intake.
Fortunately, relatively few diseases are directly caused by a single gene. A genetic variation such as APOE4 may increase your risk for an outcome, but it does not guarantee that outcome. It is just one of many factors which contribute to a complex condition such as heart disease. With lifestyle interventions (like decreased saturated fat intake), you can reduce the risk significantly. For the majority of diseases, we cannot look at single genes (or a couple of genes for that matter) and predict whether you will get sick, but we can build a model which predicts your risk and suggest interventions to reduce it.
It’s not all in your genes, however! Studies have shown that genetics explain less than 50% of the variation in nutritional responses between people. Another major factor that influences your outcomes are the trillions of “friendly” bacteria residing within your gut - your microbiome.
The cells in our gut are laid out side by side, like the bricks on a sidewalk. A healthy layer of bacteria on top of these cells functions like grout between the bricks. By acting as a physical barrier, these trillions of microbes help keep out unwanted pathogens (“bad” bacteria), maintain the integrity of our gut, and serve as a major component of our immune systems. These microbes are also able to harvest energy from indigestible carbohydrates (fiber), create helpful by-products (short-chain fatty acids, Vitamin K and some B vitamins), and help send important messages to our nervous system.
So what happens when your gut bacteria aren't doing their job? Dysbiosis is an imbalance of gut bacteria, where either the “bad” bacteria starts to overwhelm the “good” bacteria, the diversity (number of bacteria types) dwindles, or the overall numbers start to decrease. Gut dysbiosis is a predictor for metabolic conditions such as diabetes, heart disease, and stroke. The resulting “leaky gut” and low-grade inflammation can also increase the risk of immune disorders such as irritable bowel syndrome and some food allergies. The good news is that unlike your genes, the microbiome is flexible and can be influenced by our environment and dietary decisions.
So what is the number one thing you can do to help nourish these friendly bacteria? In a word - fiber. A diet rich in fiber and nondigestible carbohydrates found in vegetables, legumes, and whole grains provide the necessary nutrients required for our friendly bacteria to thrive. In return, the microbes produce compounds which decrease inflammation, improve immune function, and aid in digestion. If the bacteria don’t receive the fuel they need to survive, they turn to the carbohydrates in our gut mucus layer instead, degrading this essential layer of protection. Regularly consuming probiotic-containing foods such as yogurt, kefir, sauerkraut, and kimchi can also provide an extra boost of healthy bacteria. While, a diet high in sugar, processed oils, and artificial sweeteners can threaten the livelihood of the colonies we work so hard to build up.
Our genetics and the microbiomes may help to explain some of the nuances between individuals, but we are only scratching the surface when it comes to understanding our unique responses to food. One thing that is pretty clear is that a cookie-cutter diet just won’t cut it. It’s time to practice data over dogma and empower yourself with the facts.