There’s a lot of debate over what humans are meant to eat. Some people think plants. Others think meat. Some even think it’s tide pods.
Evolution can provide a clue.
My whole life I heard that red meat will kill you.
But I couldn’t square that circle when I looked into our evolutionary heritage. How could I possibly be sitting here today if red meat killed my ancestors? Sure, maybe it isn’t the best, but it can’t be inherently toxic or humans would never have lived long enough to get us here.
Well, I believe the same is true with regards to sugar and fructose.
After about 2 years on the carnivore diet, adding fructose back to my diet revamped my health. And looking into our physiology provided a clue why.
Diets should be informed by a number of things, one of which is what our bodies are adapted to eat.
I’ve wrote a number of times now and think that the evidence is irrefutable that we are made to eat meat. Whether it’s the pH of our stomach, our gallbladder designed to release bile, the nutrients that are only in meat, or the animal fat our brain requires to grow, I don’t think you can be at optimal health without meat.
However, like others, I thought that this meant that we were designed to only eat meat.
But, what’s become more and more clear is that humans are extremely flexible organisms when it comes to diet (not so much hamstring flexibility).
This flexibility creates a lot of confusion as people cherry pick evidence that we should focus on one group of foods while excluding others entirely.
Here’s some of the evidence that we’re also meant to consume fruit.
#1 Visual system evolved to pick out bright sweet fruits
The researcher Stanley Coren has pointed out that our visual system is designed to pick out colors. According to him, we adapted this functionality to pick out bright, sweet fruits.
Human beings have trichromatic vision — they see blue, yellow and red. Whereas dogs and other meat eaters typically do not see color nearly as vividly.
If we just ate meat, we’d have no need for this visual acuity….other than maybe to pick out the darker liver :).
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#2 Sweetness Receptor
Humans have a much greater sensitivity to sweetness than other hypercarnivores too. Hypercarnivores are much more attuned to the taste of amino acids. Whereas to most humans (other than some rare carnivores on youtube), they find the taste of raw meat fairly bland.
This helps to answer why I couldn’t stop eating fruit roll ups as a child, but a dog won’t go near them…
Something about our evolution is particularly attuned to sweet, energy rich fruit.
Now, this doesn’t necessarily mean eating fruit is optimal…just that our bodies do desire sweetness.
Additionally, we have a taste for salt that other carnivores do not. One explanation is that fruit is rich in water and low in sodium — a necessary nutrient. Meaning, if we were eating copious amounts of fruit, we’d need to go out of our way to seek out salt to make up the difference. Whereas meat is richer in sodium but lower in water.
#3 Digestion & Gut size
Our gut is definitely adapted to eating meat…this is a big reason why the carnivore diet is so healing to your gut. One of the pieces of evidence is that when you go on a super low fat diet, you tend to develop gall bladder issues. Additionally, our acidic stomach pH is most likely because we scavenged meat that required an acidic gut to neutralize.
However, I also believe there is some evidence that our gut adapted to eating fruit.
This is where I, and many other carnivores were confused. Fruit and meat digestion is similar in a lot of ways. Unlike vegetables, digesting fruit and meat both rely on enzymes instead of fermentation.
For this reason, most of our gut track is concentrated in the small intestine, instead of the colon like Gorillas / Apes who eat more vegetables.
Our gut is actually very similar to the large brained spider monkey which gets 75% of its energy from fruit.
Our ratio of gut size to brain size is also very similar to the other frugivorous apes (unlilke hypercarnivores like lions).
In many ways, we have the guts of both a carnivore and a fruit eater — which is part of where we are unique in the animal kingdom.
#4 Stress, Liver & thyroid health
This is the main part of where I think the carnivore diet goes wrong.
Sure, fructose and sugar may not be essential. Meaning, you can survive without both. But that doesn’t mean that you shouldn’t eat either.
Why?
Because sugar and fruit are important hormonal and metabolic signals as mediated through stress, liver and thyroid health.
Based on my experience and the read of the evidence, I now believe that sugar is a vital signal to your body to ramp up metabolism because you’re in a calorie rich environment.
Whereas the opposite is true when you’re zero carb (and fasting). When you need to process your body fat for fuel (especially rapidly), it is a sign that you’re in a famine state. As a response, stress increases, thyroid slows and metabolism slows to help retain your body fat after you’ve mobilized it for fuel. This is exactly what I experienced after 2 years of carnivore and part of the reason why I’m now eating almost 1000 calories more than i was on carnivore and not gaining any weight.
Let me explain why.
A malfunctioning thyroid can be an absolute nightmare for someone seeking better health and a faster metabolism.
In these two studies of subjects on keto, the researchers both found that keto lowered T3 over time:
Keto Causes Hypothyroidism: https://pubmed.ncbi.nlm.nih.gov/28076316/
Atkins (high-fat, low-carb) Diet Reduces T3: https://pubmed.ncbi.nlm.nih.gov/32698106/
The thyroid is the main captain for all energetic processes. It is one of the main determinants of health and one of the things the keto diet damages most acutely.
This is something I noticed on keto. The longer I stayed on it, the worse my thyroid functioned and the lower my T3 levels fell.
The thyroid’s hormones regulate vital bodily functions such as respiration, heart rate, muscle strength, body temperature, menstrual cycles in women, and the conversion of cholesterol to downstream steroid hormones and protective hormones.
This switch affects the thyroid hormone status as its functioning correlates with body weight, lean mass, and dietary carbohydrate content…
According to this study, “Keto significantly reduces the levels of serum T3 levels along with a concomitant increase in reverse T3, and these changes are correlated to the presence of ketone bodies.”
Carbohydrates are essential for thyroid health. And conversely, thyroid hormones are essential to maintain and regulate carbohydrate energy metabolism.
This is because parts of the brain ultimately responsible for thyroid hormone regulation, the hypothalamus and pituitary gland, require glucose to function.
In fact, the main regulation hormone, TSH (thyroid-stimulating hormone), is partly made up of glucose molecules.
In addition to these important roles, carbohydrate intake influences the amount of T4 that gets converted to T3.
When carbohydrate intake is reduced, the conversion of T4 to T3 declines.
I also think fructose is particularly important for the liver — and this has a massive role on stress levels.
Once liver glycogen runs out, your body must activate the stress response to turn protein into glucose for the blood, and switch to fat burning to reduce glucose use. It does so by first increasong glucagon, and then later cortisol and adrenaline.
Since fructose goes to the liver first to be processed, this means that fructose preferentially fills liver glycogen stores (and glycogen storage in the other organs, to a lesser extent).
Basically, this means that fructose is helping to prevent the stress response from needing to be activated when you go without food for a little while.
This is all to say that you can probably survive without fructose…but it’s clear that your body is using it as a signal to destress
I think that this is part of the reason why eating sugar feels so good. It’s very anti-stress (as shown by this study). And maybe, instead of fighting all of our biological urges, we should accept them.
“We conclude that drinking sucrose lowers stress-induced corticosterone secretion while reducing many responses to cold;”
#5 Mineral balance
The more I research fructose, the more beneficial I realize it is — especially in relation to meat consumption.
One of the potential issues with only consuming red meat is phosphorous accumulation.
Studies show that excess phosphorous increases parathyroid hormone, has proinflammatory effects and can suppress vitamin D activation .
Fructose is protective against excess phosphorous and can help to deplete levels .
Additionally, some studies show that fructose can help with mineral retention, like magnesium.
Lastly, the jury is still out on how much vitamin C we need, but fruit is a great source and can help to cross all the t’s + dot all the i’s of mineral balance.
#6 Glycolysis
Unfortunately for low carbers, you can’t get away from glucose no matter how hard you try. This “demon” is unfortunately coursing through your blood at all times.
And like many carnivores say about cholesterol, “how could something your body produces and always has in your blood be inherently toxic”.
Realizing this was part of the way I came around to eating sugar actually being beneficial.
Similar to with having skinny legs, you have 2 approaches: you can avoid leg day all together and pretend they don’t exist, or you can get under a barbell and get them yoked.
I think the same is true with regards to glucose.
If you avoid glucose entirely, it opens you open to problems with glucose metabolism over time.
Coupled with nutrient deficiencies, stress and excess pufa intake, this is now what I believe happens with diabetes. Let me explain…
Everything you know about blood sugar is wrong.
Eating honey, in this study, lowered blood sugar. This is one of those things that’s super easy to dismiss if you want to stick to your guns, but will blow your mind if you’re willing to look at it without bias.
How could it be the case that eating sugar lowers your blood sugar?
I now believe that high, enduring blood sugar isn’t from consuming too much sugar, but is a symptom of an underlying problem. Many in the carnivore / keto world think that insulin resistance is caused by simply eating too many insulinogenic foods. But there’s now plenty of evidence that high carb diets aren’t associated with insulin resistance and in fact many cases they promote insulin sensitivity .
The problem being damaged glucose metabolism, which blocks glucose from being oxidized properly . Or high stress which is liberating liver glycogen and stored fuel to be turned into energy.
One of the reasons honey may be protective is because fructose can actually get into the mitochondria without insulin. When it does, it can help to restore the oxidation of glucose, allowing blood glucose levels to fall as their normal uptake increases.
According to this one review, fructose helps fuel the liver and helps it to properly dispose and digest glucose.
Other studies show that fructose and sucrose increase metabolic rate and can help restore some of the deficiencies in carbohydrate metabolism which occur with aging.
All in all, there is now some evidence I’ve reviewed that fructose can help with glucose metabolism and actually lower blood sugar.
Conclusion
I no longer think there is “one single ancestral diet”. I think that over the course of 30 million years, all of our bodies adapted to a number of different environments.
Fat, meat and organs were critical for the nutrients to develop our large brains.
But fruit and sugar were very beneficial to signaling to our body that we were in a caloric rich environment.
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