The Zero Carb Diet: Healthy or Harmful?

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Girl eating belly pork - zero carb dieter.Over recent years, zero carb has taken off and it’s rapidly growing in popularity.

There’s certainly no shortage of people claiming to enjoy the benefits of the zero carb lifestyle.

But is a carnivore diet for humans healthy?

Is it ideal?

Or is it potentially dangerous?

This article takes a balanced look at the zero carb diet and the benefits, risks, and health impacts.

What is a Zero Carb Diet?

By its very nature, animal foods form the basis of the zero carb diet.

However, a zero carbohydrate diet plan can take several forms.

While some people concentrate on meat, others eat a wider variety of foods such as eggs, cheese, organ meats, and seafood.

The diet tends to be high in both fat and protein, and there are a wealth of success stories showing the important benefits the diet can have.

Specifically, zero carb dieters achieve significant results regarding weight loss, satiety, and better mental well-being.

On the other hand, there are many unknowns about the diet. In particular, potential long-term adverse effects are a concern for some.

Later on, this review will investigate both of these points in further detail.

Key Point: Zero carb diets completely restrict carbohydrate and focus on fats and protein. Many people believe they provide great health benefits, but others feel they are dangerous.

A 'no carb' sign - carb restriction.What Foods Have No Carbs?

Some people follow the “eat meat, drink water” mantra and eat nothing other than steak and water.

Others consume a greater variety of foods, from various types of meat to bacon, organ meats, eggs, cheese, and coconut oil.

It’s worth noting that not all these foods are actually zero carb—eggs come in at 1g carbohydrate—but they are close enough.

Here is a list of zero carbohydrate foods;

  • Bacon
  • Beef
  • Butter
  • Cheese
  • Chicken
  • Coconut oil
  • Duck
  • Eggs
  • Fish (mackerel, trout, salmon, and sardines for omega-3)
  • Ghee
  • Lamb
  • Lard
  • Olive oil
  • Organ meats (heart, kidney, liver)
  • Pork
  • Sausages
  • Shellfish
  • Turkey
  • Venison

While all these foods are “allowable” on zero carb, many advocates emphasize beef as a staple for its superior nutritional profile.

Key Point: A no-carb diet menu can involve lots of different foods. These are predominantly foods from the animal kingdom, but plant-based fats are also possible.

Is There a Historical Argument For Zero Carb?

Picture of a caveman eating red meat or beef.

With the explosion of the ancestral health scene over the past decade or so, the foods our ancestors ate is an evergreen topic of discussion.

On that note, think back to the prehistoric days and a caveman tucking into a slab of meat is a typical image.

And it’s accurate imagery too; as a species, humans have been eating meat for tens of thousands of years.

Despite vegan activist groups vehemently protesting this, there is a wealth of evidence to support ancient people being meat eaters (1, 2, 3, 4, 5).

An interesting hypothesis worth reading is ‘The Carnivore Connection,’ which views carnivory as essential to recent human evolution.

In particular, the authors believe that (6);

  • Low carbohydrate, high protein diets dominated the previous two million years of evolution.
  • For a large amount of this time, dietary carbohydrate was scarce due to successive ice ages.
  • Insulin resistance genes developed to give a survival advantage in response to lengthy low-carbohydrate periods.
Key Point: Humans and our ancestors have been deriving energy from animal foods for millions of years. It’s likely that some societies will have been zero carb for significant periods during this time.

But…Ancient Humans Ate Plant Food 

Picture of a caveman eating a tomato - humans always ate plant food.

Hunter-gatherers often lived through times of famine, and they ate what they could to survive.

Would they pass up some juicy berries they came across? Not likely.

Also, much of our modern evolution reportedly took place in Africa, a region with thousands of different species of vegetation.

Outside of the ice age periods, there would have been sufficient plant food available.

It’s highly unlikely people would pass this up, especially during times of hunger.

As a large source of energy, it’s certainly likely that ancient man valued meat more than plant foods.

However, this doesn’t mean plant foods played no part in the diet. Further, the majority of evidence indicates humans are natural omnivores and had different diets depending on their location and environment (7, 8, 9, 10).

Key Point: When we theorize on our ancient history, it’s hard to provide a 100% accurate portrayal of life. However, it’s highly likely that most humans ate plant food when available.

Is Restricting Vegetables Dangerous?

A picture of broccoli looking evil - most vegetables contain anti-nutrient.

A zero carb diet obviously involves cutting out vegetables.

Vegetables (especially greens) are very high in nutrient density, and the media constantly bombard us with messages about their health properties.

As a result, the majority of the health-conscious population would probably react in horror to the idea of restricting them.

But are vegetables really so necessary?

Vitamins and Minerals

First of all, we have to forget the myth that vitamins and minerals only come from plant foods.

They do not.

In fact, animal foods are some of the most nutrient-dense in the world.

For example, here are the nutritional profiles of apples, eggs, kale, and liver (11, 12, 13, 14).

To make it fair, the value is the RDA % per 100g;

Nutrient Apple Egg Kale Liver
Vitamin A 1% 10% 272% 634%
Vitamin C 8% 0% 68% 3%
Vitamin D 0% 8% 0% Low
Vitamin E 1% 5% 4% 3%
Vitamin K 3% 0% 1021% 4%
Thiamin 1% 4% 4% 13%
Riboflavin 2% 24% 4% 201%
Niacin 0% 0% 2% 88%
Vitamin B6 2% 6% 7% 51%
Folate 1% 9% 3% 63%
Vitamin B12 0% 21% 0% 1176%
Pantothenic acid 1% 14% 0% 71%
Calcium 1% 5% 7% 1%
Iron 1% 10% 5% 36%
Magnesium 1% 3% 5% 5%
Phosphorus 1% 19% 3% 50%
Potassium 3% 4% 7% 10%
Sodium 0% 12% 1% 3%
Zinc 0% 7% 2% 35%
Copper 1% 5% 8% 714%
Manganese 2% 2% 21% 18%
Selenium 0% 45% 1% 18%

As shown above, both animal foods and plant foods can contain high amounts of vitamins and minerals. Organ meats are especially nutritious.

Many people presume that zero carb diets are going to be severely deficient in many nutrients.

However, it is certainly possible to get most essential nutrients from eating a range of meat, seafood, eggs and organ meats.

On the other hand, antioxidant vitamins C and E are particularly difficult to obtain from animal foods.

Key Point: Animal foods are just as nutritious as plant foods are – if not more so. It is possible to get most essential nutrients from a varied zero carb diet.

Are Nutrient Deficiencies Important?

Picture of a girl thinking about nutrient deficiencies.Many zero carb proponents point to accounts of people eating a meat-only diet for 15-20 years with no evidence of harm.

In addition, our biological need for certain nutrients drops as our carbohydrate intake lowers.

For example, we don’t require the numerous vitamins involved in energy (carbohydrate) metabolism when we are consuming no carbs (15, 16, 17).

Despite this, we should remember that while anecdotes are always valuable and relevant, they are not evidence.

We can’t prove the long-term safety of zero carb simply because we don’t have sufficient research.

Also, chronic health problems typically develop over decades, so we can’t assume that 15-20 years of feeling great is predictive of the future.

This does not mean that a zero carb diet can’t be healthy in the long-run. It could well be, but we don’t have much evidence now.

Key Point: Low intake of certain nutrients may not be as important on a zero carb diet.

Polyphenols and Antioxidants

Picture of a raspberry attached to a stem.Polyphenols are biologically active compounds naturally found in plants, and particularly good sources include cacao, berries, olives and red wine.

These polyphenols have antioxidant properties, and evidence from randomized, controlled trials (RCTs) shows that they help fight oxidative stress and aging-related illness (18, 19, 20).

No matter how we cook food, we can expect some degree of oxidation, and oxidized-LDL is a major risk factor for cardiovascular disease.

Notably, numerous studies—including RCTs—show that consuming polyphenols alongside meals;

  • Prevents biological processes in the stomach that lead to LDL oxidation (21, 22).
  • Creates oxidized-LDL antibodies (OLABs) in response to the presence of oxidized LDL (2324).
  • Polyphenols from tea, herbs, and red wine can inhibit the formation of heterocyclic amines (HACs). These compounds are “likely carcinogens” and can occur when cooking meat at high temperatures or to a well-done stage (25, 26, 27).
Key Point: A wide body of evidence shows the health benefits of polyphenols. Zero carb diets don’t include food sources of these compounds, although some people consume olive oil and red wine.

What Are the Health Benefits of Zero Carb Diets?

Picture of a zero carb dieter eating steak.

As with any diet, there are several pros and cons of a carnivorous diet.

Firstly, zero carb diets have a range of health benefits.

In general, these are somewhat similar to the carbohydrate-restriction benefits of a ketogenic diet.

However, the effects are likely more powerful due to the further restriction of dietary carbs.

A typical zero carb diet should result in;

  • More efficient weight loss: most people experience significant weight loss results; a reduced body fat percentage and losing weight around the waist is common. Additionally, carbohydrate restriction has a superior impact on weight loss and metabolic syndrome risk than low-fat diets do (28, 29, 30).
  • Better mental wellbeing: very low carb diets tend to result in better cognitive performance, improved mood, focus, and mental clarity (31, 32). 
  • Reduction in food cravings: ultra-low carb diets massively improve satiety and reduce food cravings (33, 34).
  • Decreased triglycerides, higher HDL: higher levels of dietary fat and lower levels of carbohydrate reliably increase HDL and reduce triglyceride levels (35, 36).
  • Reduced blood glucose: restricting carbohydrate reduces and stabilizes fasting blood sugar levels (37).
  • Less digestive issues: reducing carbohydrate tends to improve gas, bloating problems and heartburn. On this note, many people turn to the zero carb diet after unsuccessfully trying to resolve sometimes severe digestive issues.

The Bacon Experiment

Picture of a crispy rasher of bacon.

Okay, we shouldn’t take this as evidence, but there was an interesting trial undertaken by one man.

What he did was…eat bacon.

For 30 days. Nothing else – just bacon!

The results?

  • 20 pounds of weight loss
  • Improved cardiovascular health markers
  • Lower blood pressure

These results don’t prove or verify anything—and it’s not a diet I’d recommend—but it does upset the conventional fear of meat as some kind of “artery-clogging” food.

In fact, study after study shows that meat consumption and animal fat increases HDL and reduces triglycerides (35, 36, 37).

For those unaware, these health markers are likely the most protective against cardiovascular risk (38).

Key Point: Ultra-low carb diets tend to improve health markers such as blood sugar and triglycerides. Additionally, they are great for satiety and managing food cravings.

Are There Any Health Risks?

There don’t appear to be any immediate health risks from zero carb diets, other than typical ‘keto flu’ style symptoms.

In my personal opinion, there’s no reason to suspect that zero carb dieters can’t enjoy long-term health benefits.

However, there’s also no evidence of long-term safety.

Is it Sustainable?

Family having dinner around the table at Christmas.

One of the biggest problems with all diets—whether vegan, paleo, keto or zero carb—is sustaining them.

Pizza delivery with friends? Well, that’s a difficult ask even for a strict paleo dieter.

This lifestyle struggle only multiples with zero carb, since the diet rules out almost all non-animal foods.

Eating no carbs at all certainly has an effect on social events.

For instance, occasions like birthdays, Christmas dinner, Eid al-Fitr, or a night out with friends or family become much tougher.

Do-able, certainly – but tougher.

On the positive side, zero carb foods such as bacon and beef are delicious and make the limited food choice easier.

And many people are sustaining the diet – both because they love the food and feel it is making them healthier.

Key Point: Sticking to a zero carb diet will be difficult for some due to social occasions.

Zero Carb: Healthy or Harmful?

Personally, I think that a zero carb diet is much healthier than the processed stuff most people are eating.

I also believe that the diet is unlikely to be harmful – especially if well-formulated.

However, there is so much evidence for the health benefits of foods like cacao, berries, avocados, olives, mushrooms, and seaweed.

Sure, it might be possible to find a study or two about anti-nutrients in these foods.

But the overwhelming body of evidence points to them having substantial health benefits.

To sum up, I don’t think a zero carb diet is harmful.

But personally, I think a diet that includes a variety of nutrient-dense animal and plant foods is optimal.

8 COMMENTS

  1. Not to nitpick, but all that “vitamin A’ in kale is beta carotene, a precursor, not preformed retinol. So if you’re lacking or deficient in the enzyme dioxygenase, you’re not going to utilize that “vitamin A” especially if you’re on a low fat diet. Also with the vitamin K, you really have to break that down into K1 and K2 since kale is a good source of the former while grass fed beef liver is a good source of the latter. Kale doesn’t have any K2.

    • Hi Stefhan,

      Thanks for the comment!

      You’re quite correct – animal foods are much better sources of fat-soluble vitamins.

      Unfortunately the nutrition database doesn’t track K1 and K2 otherwise I could have split them.

      I thought explaining it might start going a bit off-topic, but I suppose it’s important so I’ll add a line or two in there.

  2. Nicely balanced article. The only additions I could suggest would be a comment on fiber and possible digestion issues. Also the high levels of protein and mTor pathway activation. They could be the chronic problems down the road, however, we won’t really know until someone studies it with high N values.

    • Thanks John.

      And I agree.

      I think regarding fiber, that one goes both ways… a few people have trouble when they first cut down on it but others are perfectly fine.

      On the other hand, fiber can actually be problematic in some cases…especially for some with digestive problems.

      That’s basically a whole new topic though!

  3. Animal foods take long time to digest and also chances food getting putrid during long journey from oesophagus to small intestine.. it takes anything between 24 to 48 hrs for animal food to digest. However vegetarian food may take 12-24 hrs to clear through all intestines & light on stomach.While animal food doesn’t increase blood sugar level , it would increase insulin resistance and whereas carbs like
    Potatoes and rice would elevate the blood sugar level. Fibre in plant food would aid in colon cleansing. My view is that we should restrict carb intake to 25% of total food intake

    • Hi Sushil,

      I think all of those things are open to interpretation – for example, some struggle without fiber while it can aggravate the GI tract for others.

      Personally, I can digest meat really easily but I used to struggle when I used to eat large amounts of grains in my student days. There’s also no reason why meat would increase insulin resistance in the context of a very low carb diet – if you mix fatty meat with excessive amounts of carbohydrate then that’s asking for trouble though. Most healthy races have generally been high carb OR high fat – usually not both together like the modern diet.

      25% of total food intake sounds like a good mark to aim for.

  4. Thanks Micheal
    The issue of insulin resistance is more to do with consumption of meat products..,nothing to do with low carb diet..So for diabetic patients currently to reverse diabetes doctors recommend to abstain from meat and migrate to plant protein and stay at 25% carb intake. Infact they strongly suggest to avoid fish and limit protein to lean chicken. India and USA has large population of diabetics. Indians eat large amounts of carbs and Americans eat large amounts of meat along with high glycemic sugary food and animal and dairy fat . Also human beings by design have a long intestines designed to eat fibrous food and whereas carnivores have small intestine to quickly purge the waste arising of meat post digetion of meat..So my question is whether humans by design are omnivores/ herbivores or carnivores???

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