The gut's surface area is about 400 square meters, approximately the size of a basketball court. It requires 40% of the body's energy expenditure and is renewed about every 5 days (Bischoff, 2014).
Nutrition is so central to our health, it's no wonder that dieting and weight loss is big business—it's a $72 billion dollar industry in the U.S. alone.
What works for one person may not work for another. Instead, there is a diet that works optimally for your individual genetics, gene expression, metabolic state, microbiota, exposure profile (environment), lifestyle, and physiology at a given time. The challenge lies in figuring it out amidst the ever-flowing changes...
A healthy amount of food skepticism is warranted, especially when incorporating new foods that historically weren't a part of our ancestors' diets. Indigenous people tend to have very healthy gut microbiomes and immune systems compared with the average Westerner, and there's a movement towards "re-wilding" the gut microbiome. Pesticides and other contaminants can also adulterate our food, lowering its nutritional quality. Our food can slowly heal us or slowly kill us.
Diet alters feedback loops, changing our gene expression, overall health status, and nutritional requirements.
Here are 11 reasons there isn't "one diet" that works for everyone.
Overview
1. Food allergies and intolerances
"One man's food is another man's poison."
It's estimated that up to 20% of the world's population may have a food intolerance.
A diet that one person swears by may sicken another and nearly land them in the hospital.
What one person deems a superfood can give another person skin breakouts.
You can develop allergies over your life, such that something that never used to bother you now gives you noticeable symptoms.
Keeping a food log can help you keep track of how your body responds to certain foods.
2. Plant toxins
An estimated 96% of Americans are omnivores. Recent archaeological evidence shows that earlier in human evolution, meat consumption, specifically in the form of fat-rich bone marrow, catalyzed the cortical expansion.
Further, plants evolved mechanisms to defend themselves from being eaten, which can be toxic to humans. This may explain why many people experience worsening health such as brain fog, bloating, and decreased muscle mass on a raw vegan diet. There are oxalates, lectins, FODMAPs, antinutrients like tannins and phytic acid that decrease absorption of minerals, and much more.
Oxalate-rich foods like spinach, almonds, and chocolate can stress out the kidneys. Lectins found in tomatoes, eggplant, and peppers can cause leaky gut in those predisposed. FODMAPs, which stands for fermentable oligo-, di-, mono-saccharides and poly-ols, are short-chain carbohydrates that are poorly absorbed in the small intestine. Fiber does not help with bloating and is not recommended for IBS or SIBO.
Certain people may be sensitive to particular plant toxins and have to avoid certain fruits, vegetables, grains, legumes, nuts, or seeds accordingly.
3. Ancestry and genetics
Geography, climate, and available food sources shape dietary choices, which affects protein expression profiles. For example, certain groups can digest milk better than others due to lactase persistence.
If someone has a family history of diabetes and kidney issues, they may restrict intake of grains and sugars, while someone with a family history of heart disease might be more cautious about eating meat.
4. Different effects imply different requirements
Some people get brain fog from eating certain kinds of meat, like turkey, and others get brain fog from completely cutting out meat, due to vitamin B12 deficiency or lack of some other nutritional requirement.
5. Performance-dependent
Elite athletes training for a marathon or extreme endurance may eat mostly protein and simple sugars (e.g. chicken, pasta, banana) and stay away from fatty foods and fiber (e.g. fish, beans, broccoli). This is because fats and fiber break down more slowly, and more blood will go to the gut, decreasing muscle performance. Carbs are also a quick source of energy. A high-carb diet may work for a triathlete but may be potentially disastrous for a type 2 diabetic patient.
6. Metabolic rate affects appetite
The food you eat and when you eat it affects your metabolism and subsequently your hunger.
To speed up your metabolism, move around, be active, eat protein, do cardio, lift weights, and get a good night's sleep. Caloric restriction, sedentary lifestyle, and delaying breakfast generally slow down metabolism.
Sugars and high-glycemic foods spike blood glucose faster, so they may not hold you over as long.
7. Gut microbes affect our food behaviors, preferences, aversions, and cravings
Diet impacts which gut microbiota thrive in the gut, and in turn, gut microbes influence sensations like satiety, nausea, and conditioned food aversion, creating a feedback loop of dietary preferences. Around 90% of the body's serotonin and 50% of the body's dopamine is produced in the gut, emphasizing the role of gut microbes in food-related mood and reward pathways.
Since gut microbes modulate the vagus nerve, part of the autonomic nervous system, a lot of our response to food is not conscious. A person who once enjoyed the taste of greasy food could later find the smell of fried fast food nauseating because of the gut's memory of that food wrecking their digestion, or simply because their gut microbial profile has changed.
Intuitive eating goes beyond the taste buds' addiction to sugar, salt, and fat, and it considers how we feel minutes to hours to days after we eat.
8. Sustainability of restrictive vs. diversified diets
Many people grow bored of eating the same thing every day, week, or month. This makes it harder to draw conclusions from diet data. Omnivores become semi-vegetarians, vegans become pescatarians, people cut out gluten or dairy for health reasons. Seeking out the nutrients our bodies need from diverse sources helps keep dieting enjoyable rather than restrictive.
9. Chronic and infectious diseases modulate gut-blood-brain integrity
Certain disease statuses can alter the microbial composition and create a need for specific dietary interventions tailored for each case.
For instance, most people are recommended fiber-rich diets for the short-chain fatty acid (SCFA) metabolites and their effects on immunity and brain health. However, fiber may upset digestion and exacerbate inflammation in some people, including those with IBD and Crohn's. It's important to note that fiber isn't causing the disease. IBD patients may see improvement of symptoms on a low fiber diet due to a different gut microbial profile, and they should read about the low FODMAP diet, specific carbohydrate diet (SCD), and the GAPS diet.
Patients with a compromised blood-brain barrier due to leaky gut, autoimmunity, or active viruses should be take caution when consuming metal chelators such as chlorella, spirulina, or cilantro, because it can redistribute heavy metals like mercury to the brain. People without these conditions don't need to be as concerned with avoiding these particular foods.
I recommend taking a gut micribiome test, such as Viome, which reveals patterns in biochemical pathways and can tell you if your gut lining is compromised and which viruses may exist in your gut.
10. Lifelong variations
Our diet varies continuously throughout our lives and even on a daily basis. What we want and need can change over time. We seek out different foods at age 10, 20, 40, and 60. Kids have more sensitive taste buds and high energy, often leading them to prefer bland and carbohydrate-rich foods like mac 'n' cheese. What a 20-year-old finds salty, a 50-year-old may find perfectly seasoned.
11. The nutritional entourage effect
Many studies comparing diets contradict each other. They don't take into account the complex interplay between activity levels, food type, caloric intake, timing of eating, genetics and gene expression (intestinal transporters, immune biomarkers), metabolic rate, nutritional status, and gut microbial composition.
Several studies show that different low-fat and low-carb diets don't show a significant difference in weight loss. More people drop off low-carb diets like keto, likely due to our body's preference to use glucose as fuel—the restriction can even cause weight to rebound and overshoot. It seems to be more important where we are sourcing these nutrients from. Specific foods seem to matter because of synergistic interactions between their constituent molecules, known as the entourage effect. Supplements may not work for some people because they lack nutritional diversity, enter in the wrong part of the pathway (e.g. too far downstream and not at the root cause), lack bioactivity, have unwanted side effects, are not compatible with host biochemistry, are too high of a dose, or contain toxic contaminants.
Key takeaway
Factors that contribute to the optimal diet at a given time include:
individual genetics
gene expression, e.g. intestinal transporters and receptors
food behaviors: food preferences, timing of eating, caloric intake
nutritional quality and food purity, including soil quality where food is grown
endocrine factors: gut microbial composition, hormones
immune biomarkers: inflammation, infections, autoimmunity
metabolic rate
activity and energy levels
body composition