Should You Add Fruit To Your Carnivore Diet?

Meat And Honey

Get strapped in for a bit of controversy, because the question of fructose is hotly contested in the carnivore sphere. On one side, you have the folks who see fruits as the mildest in toxins, as well as a fix for the potential side-effects that come with long stints in ketosis. Then we have the other, where carbs are poison no matter the form, and ketosis is a viable long-term strategy. Finally, there’s the third side, for the people who aren’t particularly, or are blissfully unaware that there’s a war going on.

I’d like to make the case that, while there is a place for carbs on the human performance cuisine, you probably shouldn’t start with fructose. To put it simply, there are better options than guzzling raw honey all day.

Is Fruit Ancestral?

Carnivore’s biggest selling point is its status as an ancestrally appropriate diet. The vast chunk of the human timeline was spent in the paleolithic, before the glacial barriers melted and the agricultural revolution began. Over that span of several million years, we evolved into what was effectively the finished article. Since agriculture’s dawn, the changes have been more cultural than physical. So it stands to reason, that any specialisations towards food groups would have been bedded in across that period, which in turn would have been dependent on what foods were regularly available to us.

Now there is plenty of evidence to suggest that red meat was the star of the paleolithic platter. That much shouldn’t be up for debate. Then there’s fruit, which was certainly available, but that comes with several major caveats.

1. They Weren’t Very Edible

The apples you’ll be picking up in the supermarket would look drastically different from one being plucked from the forests of Kazakhstan, where the wild ancestor to the forbidden fruit is found. The Malus sieversii is smaller and more acidic, a less glamorous prospect than its supermarket equivalent. 

Wild bananas and watermelons were mostly seeds and little flesh. Peaches from 4000 BC would have resembled salty cherries, where you’d basically bash your teeth against stone. The ancestral fruits available to our hunter-gatherer ancestors would have offered much less sugar, and much more indigestible fiber.

Since then, we’ve genetically engineered fruits to become far more palatable, lending some a fanciful notion that the paleothic era was a garden of eden, the landscape littered with sweet fruits and plump vegetables all within a morning’s walk from whatever cave you woke up in. 

Unfortunately, in the harsh realities of our pre-agricultural brethren, foraging would have been an extraordinarily time-intensive activity. Research suggests that it would have yielded around 1000 calories per hour. Compare that with hunting, which netted 10,000 calories. When the principal game is survival, it wouldn’t seem right to go picking pears when you’ve spotted fresh footprints left by a giant ground sloth. The economics wouldn’t allow it. 

The fact is, modern fruits are basically GMO crops. Over thousands of years, the best seeds have been picked to engineer the fattest fruits with the sweetest flesh. They look nothing like their seedy, fibrous, and bitter paleolithic predecessors.

2. They Were Seasonal

If you like your strawberries, then you’ll be happy to know that the UK season now lasts 20 weeks, thanks to some greenhouse innovation. Back in 1990, it lasted just 6 weeks. Beyond that brief spell, you’d be relying on Mediterranean imports to soothe your strawberry cravings. It wouldn’t taste quite as good, and there’s that whole chestnut of environmental pollution through a few thousand food miles, but it’s better than just eating cream. 

Believe it or not, our paleolithic ancestors didn’t have the luxury of bringing in foreign imports to pave the difference when their favourite fruits were out of season. Global trade just wasn’t a thing, even local tribes would have rarely traded with each other, and they would have kept it to raw materials. The refrigerator wasn’t a thing back in the ice age either, putting another dent in their chances of transporting peaches across continents.

The fruits that our ancestors could find, fiber and all, would have only been available across a few months at most. Beyond that, they’d have no choice but to put their ethics aside, and chase their dinner across the steppe.

You might be wondering where honey fits into all this. It’s not really seasonal, although bees typically shut shop over the winter. Our ancestors certainly had the means to access honey, but nevertheless, the domesticated beehive wasn’t invented till the mid-nineteenth century. 

The Hadza tribe in Tanzania, one of the last hunter-gatherers still roaming the planet, definitely have their fair share of honey. But while looking at present-day hunter-gatherers certainly lends us a window into the paleolthic past, it needs a fistful of salt. 

Modern hunter-gatherers operate in an environment that’s been severely depleted of resources. The megafauna of old are either long extinct, or protected from hunting. The animals left on the menu are smaller, leaner, and harder to catch. If anything, tribes like the Hadza represent the closing notes of the paleolithic, when the poisoned chalice of agriculture became necessary for the continued survival of the human species.

I’m not arguing that our paleolithic ancestors didn’t nibble on wild berries or swindle beehives. They certainly did. Just not across the year, and not in significant amounts. The merits of fructose don’t have much to ride on from an evolutionary context. If you wanted to match the steps of your ancestors, then you’d be best off saving fruit and honey for a few weeks in the year. Preferably from late summer to mid-autumn, and preferably during bulking season. But don’t act on that just yet, because there’s another angle we have yet to cover.

How The Metabolism Responds To Fructose

We’re not done with evolutionary biology just yet. In the spirit of providing context and a possible explanation for the mechanisms we’re about to unravel, it’s worth weighing up the fact that fruit season arrives at an opportune moment, right before winter begins to sink its miserly claws. In the spirit of surviving across months of food scarcity, it paid to be able to amass and store excess energy. 

Fruit appears to have filled that evolutionary role, by placing the body in a state of energy depletion, and encouraging lipogenesis (the fancy word for getting fat). In the context of living through the harsh winters of the last ice age, fructose may well have helped ensure the survival of the human species. For us modern folks, blessed with food in abundance across the seasons, it doesn’t bode so well. In fact, fructose has been labeled as a ‘key factor in the development of metabolic syndrome’.

What makes fructose different from other sugars? Fructose and glucose may appear to be quite similar, but once they get ingested, they take completely different paths. Glucose stimulates insulin secretion, upon which, in a healthy system, they can be swallowed up by the muscles. 

Fructose, on the other hand, doesn’t prompt an insulin response. It gets sent to the liver instead, where it bypasses two rate-limiting steps in glycolysis, glucokinase and phosphofructokinase. So that’s already laying down the groundwork for overconsumption. Things only get worse from there.

Fructose is eventually metabolised by fructokinase, which has no negative feedback system, and uses up ATP (the basic energy currency in the body) for phosphorylation. This in turn creates a depletion of ATP, subsequently leading to a need for more fructose to plug the gaps, as well as the formation of uric acid as a byproduct. 

Uric Acid – The Survival Switch

You might just associate uric acid with gout, but that’s only one of many unsavoury outcomes that have been tied to high uric acid levels. Besides being a known risk factor in hypertension, it has also been linked to insulin resistance and endothelial dysfunction. It’s a toxic byproduct that causes oxidative stress in the mitochondria, leading to the aforementioned metabolic dysfunction.

Why does uric acid cause so much damage? As it happens, this byproduct may well be the primary driver of the aforementioned survival mechanism. Uric acid is a bioactive compound that affects fuel partitioning, by increasing oxidative stress and hastening triglyceride generation. It also amplifies fructose absorption by upregulating fructokinase. The net effect, the body gets to pack on more blubber. Factoring in its ability to act as an antioxidant when outside the cell, how it maintains blood pressure during times of low salt intake, how it increases temporarily in response to carbohydrate restriction, and you get the picture. High uric acid levels allowed our ancestors to survive across periods of famine. An essential mechanism that’s now proving costly in the modern context of food abundance and high fructose.

Then there’s the whole mechanism by which fructose itself can hasten lipogenesis. When the liver gets overloaded with fructose, it proceeds to store the excess calories as fat instead, which can lead to fatty liver disease. Given that the liver can only store about 80 grams of glucose at any one point, it doesn’t take much to flip the switch.

In short, fructose doesn’t have any impact on satiety, doesn’t replenish muscle glycogen, and leads to harmful byproducts. 

None of this is necessarily a death knell for your chances of eating fruit and living to tell the tale. Flooding the liver with fructose will certainly give you a bad time, but you’re not getting there by eating an apple, which gives you around 13 grams of fructose. A can of coke, on the other hand, contains 30 grams of fructose, and chances are you’re not stopping at one. Fiber ameliorates the process by slowing down the passage of fructose, allowing the liver time to break down and metabolise incoming food. 

Honey is a little more suspect, containing 9 grams of fructose in a tablespoon serving. Tropical fruits also have more fructose than their northern counterparts. There’s certainly merit in, if not avoiding, then at least moderating your fructose intake. As for fruit juice, forget about it.

As for uric acid, the safe upper level has been marked down as 7.0mg/dl for men, and 6.0mg/dl for women. That being said, slightly lower levels will likely still harm those who already exhibit markers of metabolic dysfunction, such as visceral fat accumulation. Uric acid can also be created endogenously, meaning without the need for incoming fructose, and that process gets exacerbated by insulin resistance. To pile onto that, meat is high in purines, which breaks down to form uric acid. In particular, organ meats like liver, as well as sardines and anchovies. 

The point of all this? If you’re still metabolically unhealthy, or just consuming large amounts of meat, then there are plenty of reasons to be wary of fruit. Staying away from fruit juice and High Fructose Corn Syrup only gets you so far. Honey offers a boatload of fructose, and shouldn’t be seen as benign. If you’re eating a pound of liver a week, that may well be generating inflammation that you’re better off without.

There’s still one more angle to cover.

Is Ketosis Harmful?

A ketogenic diet like carnivore doesn’t need long to work miracles. For its effects on boosting energy, stabilising the gut microbiome, restoring mental acuity, and torching fat stores, ketosis presents a fantastic proposition. But the question many people continue to pose, is whether such a stressful, restricted state can be taken over the long run. And the answer many arrive at, is to bring back the holy grail of metabolic flexibility with fruit and honey.

In one technical sense, they have a point. Ketosis is stressful on the body. It upregulates AMPK and NRF2. Two pathways that have been associated with longevity. Over the paleolithic, ketones would have helped us survive periods of fasting between successful hunts. That being said, stress simply can’t be categorised as a negative. It can break, but it can also make. That’s the principle of hormesis, also known as anti-fragility. 

The source, the acuity, timing, frequency, the response, all these can determine at what dose hormetic stress gets upgraded into poison. Since we’re considering a mechanism that was likely the default energy mode of our ancestors, it’s hard to imagine that extended time in ketosis is in any way dangerous.

Long-term ketosis has been associated with lowered T3, the active thyroid hormone. Yet it also increases sensitivity to T3. Then there’s the case of low free testosterone, which would certainly be of concern for barbell chasers like me. At this point, it’s still quite murky. 

While some blood panels of long-term carnivores show lowered free testosterone, which is the type that the body can actually use to get you jacked, there’s conflicting evidence of very low carb diets raising testosterone significantly. Not to mention the fact that high insulin raises sex hormone-binding globulin (SHBG), which lowers free testosterone. Insulin resistance itself is associated with low testosterone, and guess what diet is the most proficient at reversing it?

Don’t get the wrong idea here. There are certainly some perks to bringing low toxicity carbs into a carnivore diet. But that’s in the grand scheme of achieving peak physical performance in a system that’s already metabolically healthy. For those who are happy to take a slight dent on their muscle-building potential, there’s little to suggest that the zero carb template can’t go the distance.

And if you just want to get your hands on phytonutrients, just grab some grass-fed red meat instead. There’s plenty.

As for the many benefits of ketosis, any decent amount of fructose will offset them by loading up on liver glycogen. That leaves you in energy purgatory, where you’re still very low in carbohydrates, but unable to use fats to their fullest potential. If you’re already fat adapted, you can probably get by in such a state, while not seeing the fullest potential of your carnivore diet. But if you’re still green to ketosis and the body’s fat-burning mechanisms are still somewhat dormant, this is probably going to devolve into an absolute grind.

Summing Up The Pros And Cons Of Fructose

Benefits of adding fructose

• Relatively low in toxins
• Can be tasty
• Adds colour and variety to the plate
• Harmful effects can be mostly attenuated by fiber

Downsides of adding fructose

• Still include toxins
• Can still be harmful for those in a state of metabolic dysfunction
• Don’t include critical nutrients you can’t get elsewhere
• Can block the beneficial effects of fructose

Fruits do tend to be lower in toxins. Raw honey does have medicinal properties. They may look like prime candidates for bringing some colour back to the carnivore diet. But just like with anything else in the metabolic landscape, there are a few nuances to hurdle past. Fructose is toxic to the body when allowed to flood the system, and even small amounts can be costly when you’re still fighting off metabolic dysfunction.

Personally, I’d rather opt for glucose in the form of white rice and cluster dextrin, which can go straight to the muscle, assist glycogen repletion, buffer performance, and get me yoked. That being said, mangos are delicious, so it’s your call to make.