It is common for people to be skeptical of a low-carb diet in the beginning, especially since high-carb, low-fat advice has been so prevalent for decades.
We don’t want any unsubstantiated fears to get in the way of people reaping the benefits of a low-carb diet. In this guide, you will learn why many of these controversies are based on misunderstandings or incomplete knowledge.
However, our goal of making low carb simple also requires us to be upfront and honest about potential problems and how to handle them; some adverse effects can and do occur on low carb.
Here are the most common controversies about low carb and what the best available scientific evidence can tell us about them.
1. Will saturated fat clog my arteries and give me a heart attack?
No. This is probably one of the biggest nutrition myths of the last few decades.
First of all, the mechanisms by which we develop heart disease are not analogous to the way a sink develops a clog. There are many potential contributing factors to the development of heart disease, including genetics, inflammation, and metabolic health conditions, such as diabetes. Further, the interaction of diet with these other variables can vary greatly from one individual to another.
In terms of scientific evidence, links between saturated fat and heart disease are weak and inconsistent. Although some reviews of the literature do find a weak relationship, an increasing number of meta-analyses and systematic reviews find that there is no significant connection between saturated fat and heart disease. The weakness of the evidence against saturated fat is catching on in the mainstream media as well.
Because the evidence is so weak and because the individual response to dietary fats varies significantly, population-wide recommendations to avoid saturated fat may have been a mistake.
Watch doctors explain why saturated fat is neutral
2. Does a low-carb diet cause high cholesterol?
Low-carb diets tend to improve the cholesterol profile by increasing levels of HDL (“good”) cholesterol and decreasing levels of potentially harmful triglycerides. They may also improve the size profile of the LDL particles.
These beneficial changes in the lipid profile are also associated with decreased insulin resistance, suggesting that overall health is likely improved.
Regarding LDL (“bad”) cholesterol, most people experience no significant changes on low carb.
However, in some people, LDL levels decrease or (more often) increase somewhat.
A minority of people will see their LDL cholesterol increase dramatically on a low-carb, high-fat diet. In this situation, it may be worth adapting the diet to lower LDL. Depending on your overall risk profile, you may want to work closely with your doctor to monitor for any evidence of cardiovascular disease.
To learn more about how to evaluate rising LDL on a low-carb diet, see our dedicated educational guides:
LDL low carb hyper-responders
Is elevated LDL harmful?
How to lower LDL on a low carb diet
The bottom line: Low-carb, high-fat diets generally improve the lipid profile and reduce most risk factors for heart disease. This effect is emphasized by a 2010 study that showed a reduction in atherosclerosis after two years on a low-carb, high-fat diet.
Low carb and cholesterol – the full guide
4. Is low carb bad for the environment?
This question needs to address the following:
1- Does eating low carb mean you have to eat more meat?
2- Is meat by definition bad for the environment?
It’s a common misunderstanding that a low-carb diet requires eating a lot of meat. This is simply not true.
A low-carb diet is just that — low carb. You can otherwise eat however you want, be it vegan, vegetarian, carnivore, or anything in between.
The amount of protein usually stays moderate — about 1.2 to 2.0 grams per kilo per day. This amount of protein may be more than many people are eating, but it doesn’t have to come from meat. It’s very possible to eat a vegetarian or vegan low-carb diet, should you want to.
Furthermore, the impact of meat production on the environment depends on many factors. Do you buy locally raised, grass fed or pasture raised meat or poultry? If so, these can be raised in a manner that is environmentally friendly! They may potentially reduce the pesticide burden and nutrient depletion of soils, as well as allowing for more carbon dioxide to be stored in the ground.
However, if most of your meat comes from industrial meat production sites, also known as CAFOs, then there may be a significant contribution to greenhouse gasses.
Finally, a low-carb diet often results in people eating less food, because it’s so satiating. After significant weight loss, people need even less food. Needing less food, and needing to eat less often, is of course good for the environment.
Bottom line: A low-carb diet doesn’t require you to eat more meat. If you choose to eat more meat, you can search for meat from regenerative ranchers, which may provide a net benefit to the environment. Eating meat from CAFOs will likely contribute to increased greenhouse gasses.
Six ways to stay environmentally friendly on a low-carb or keto diet
Diet Doctor Podcast with Professor Frank Mitloehner and another with Diana Rodgers.
TED / Allan Savory: How to fight desertification and reverse climate change
Watch one of the smartest men in the world explain the real problem for the environment (Hint: it’s fossil fuels)
5. Can you get nutrient deficiencies on low carb?
Probably the opposite is more often true. The foods consumed on a low-carb diet are highly nutritious. For example, eggs (a staple for many people on low carb) may provide the most complete nutrition of any food on the planet.
Consider that a complete chicken can be formed from the nutrients inside the egg. There’s no way for the chicken to pop out and get some vitamins and minerals while growing in the egg; everything has to be there. And by eating an egg, we humans get all those nutrients.
Meat, fish, and vegetables are also highly nutritious foods. And many people eating low carb tend to replace nutrient-poor pasta, rice, and potatoes with more nutrient-rich vegetables.
Studies show that a low-carb diet can be nutritionally complete.
Compared to the more complete nutrition of a low-carb diet, refined flour is more or less devoid of any nutrition apart from pure starch. Usually, it’s legally required to add vitamins to flour, so that people who eat a lot of it do not get vitamin deficiencies.
Also, grains like wheat are high in phytic acid that can potentially reduce the absorption of many minerals.
Another concern with low-carb diets is the lack of fruit, often thought to be necessary for proper nutrition. This is a misunderstanding. Apart from vitamin C, there are very few nutrients in most modern fruit. These days, they are modified to be large and very sweet. We think of fruit as candy from nature, which should probably be eaten in moderation. Fruit juice is even worse, given the concentrated sugar and lack of fiber to help slow the absorption.
Modern fast food and snack food also contain a lot of calories and minimal if any nutrition. And low-fat products are low in essential fat-soluble vitamins, which are found in full-fat versions of yogurt, cheese, and other whole foods.
Bottom line: Switching from a standard Western diet to a low-carb diet based on real foods is likely to significantly increase the amount of vitamins and minerals you get from your diet.
6. Can low carb damage your thyroid?
Not likely. If you eat a well-formulated low-carb diet, it’s very unlikely it will affect your thyroid negatively.
Although some studies of low-carb, high-fat diets have shown a decrease in the active thyroid hormone T3, it seems unlikely that this represents a clinical problem. For instance, some hypothesize that our bodies become more sensitive to thyroid hormone and therefore have a different “normal” range. Others suggest fat is more metabolically efficient, and therefore less thyroid hormone is required to metabolize it. While these are just hypotheses at this point, they highlight how a change in a single lab value does not automatically signify a problem or deleterious change.
In fact, some people who lose significant amounts of weight on low carb may end up needing less thyroid medication, and a few individuals may even be able to stop taking it completely. This may just be an effect of a smaller body needing less thyroid hormone – there isn’t any research showing that carbohydrate reduction itself can improve thyroid function.
This means that if you have hypothyroidism and supplement with thyroid hormone, you can start a low-carb diet like anybody else and continue to do regular checkups per usual. If you lose a lot of weight, it may be wise to do an extra check of your thyroid blood tests once in a while, e.g. every time you’ve lost 30 pounds (15 kilos). It’s not impossible that your dose may need to be adjusted.
Bottom line: Eating a healthy, low-carb diet should not negatively affect your thyroid.
7. Can low carb damage your kidneys?
Highly unlikely. Many people still believe that a low-carb diet or even a high-protein diet could put a strain on the kidneys. This is a myth based on two misunderstandings.
First, a well-formulated low-carb diet is moderate in protein — around 1.5 grams per kilo per day.
As a low-carb diet doesn’t need to be very high in protein — for example, 3 grams per kilo per day — the whole “problem” behind this controversy simply does not exist.
Secondly, people with normal kidney function can handle high amounts of protein without any problem for the kidneys.
Even if people choose to eat excessive protein, this will only be a problem if the kidneys are already severely damaged. An example of this would be end-stage kidney disease that is close to requiring dialysis. If you have severe kidney disease and you’ve been told to limit protein, you should of course do so. But you might still be able to successfully eat a low-carb, high-fat diet.
To summarize: For people without kidney disease, there’s no reason to worry about the effect of excessive protein on your kidney health.
Bottom line: A low-carb diet is fine for your kidneys.
In fact, by lowering elevated blood sugars in people with diabetes, a low-carb diet may actually protect the kidneys from one of the most common causes of damage.
What you need to know about a low-carb diet and your kidneys
8. Can low carb make you depressed?
Not likely. But during the first week or two of a low-carb diet, it’s common to experience symptoms similar to those of depression (such as lethargy, tiredness, irritability, brain fog).
These problems usually disappear within a few days to a couple of weeks. They can often be avoided or mitigated by getting enough fluid and salt – for example a cup of bouillon 1-2 times a day.
Long term, a low-carb diet often has the opposite effect. Getting into ketosis can make some people feel very energetic and might increase mental performance and endurance. People sometimes mention the “mental clarity” they feel.
Studies of the mental state on low-carb diets generally show either no clear change or a slight improvement, compared to before starting the diet.
If someone does feel depressed, however, it could be related to having what resembles an addiction to reward from high-carb, sweet foods. Eliminating these high-reward foods may result in temporary feelings of loss and sadness, similar to symptoms of depression. It may be analogous to the effect of withdrawing from nicotine or alcohol when addicted to these substances.
Fortunately, after early withdrawal symptoms have passed, getting free of an addiction is incredibly liberating and enables people to lead fuller and happier lives. So it can definitely be worth the struggle.
Finally, to make a low-carb diet feel great long term requires tasty food and a simple and enjoyable lifestyle. Feel free to use our resources to speed up the process.
9. Is low carb bad for exercise?
Low carb can be good, bad, neutral or even fantastic for exercise. It depends.
During the first couple of weeks when you’re switching from a diet rich in carbs to a low-carb diet, your capacity in the gym will most likely go down. This is due to the low-carb flu and not being fully fat-adapted, but it will likely improve within several weeks.
After a few weeks of adaptation, people often report feeling at least as good as before when exercising, especially if they make sure to get enough fluids and salt.
Furthermore, for endurance athletes, there are many potential benefits to being fat-adapted and eating LCHF. For example, Chris Froome won Tour de France multiple times after adopting a low-carb diet.
But the findings are not universal. Two studies out of Australia report that race-walk times decreased after 12 weeks of eating a keto diet, despite improved fat oxidation.
When it comes to powerlifting and weightlifting, low-carb diets have demonstrated benefit. Additionally, following a ketogenic diet might improve body composition when combined with resistance training.
However, more carbs may be needed for non-endurance sports such as sprinting, etc. In these cases, it might be a good idea to take in some more carbs on the day you need to perform.
The bottom line is that scientific evidence is mixed on how ketosis affects athletic performance. Individual variability, different effects for different types of exercise, and the importance of fat-adaptation all need to be taken into consideration.
Watch doctors explain how low carb can be good for exercise
Learn more about how to increase physical performance on low carb
10. Is low carb bad for your gut bacteria?
Probably not. There is currently a lot of research being conducted about gut bacteria and the microbiome. The main problem with much of the reporting on gut bacteria and diet is the confusion of statistical correlations with causality, i.e. taking weak clues and mistakenly calling them proof.
Not much can be said about the health effects of changes to the microbiome on a low-carb diet — only that it changes. However, many people report that they have less gastrointestinal distress and bloating after starting a low-carb diet.
Watch a presentation on the possible benefits of slow carbs to feed the microbiome
11. Can you get constipated on low carb?
Yes. Constipation is a possible side effect that can occur, especially during the first time on a low-carb diet, as your digestive system may need time to adapt.
It can usually be alleviated by either drinking more water and increasing salt intake, taking in more fiber or, if necessary, adding Milk of Magnesia.
Note that just because some people have a bowel movement less often does not mean they are constipated. Many people report decreased stool frequency on low carb, but as long as they don’t feel bloated or have abdominal pain, it isn’t a concern.
It’s important to note that, if you do suffer from constipation when starting low carb, it will usually be temporary.
Learn more about preventing or curing constipation on low carb
12. Can you get osteoporosis on low carb?
No. There is a lingering idea that eating a diet low in carbohydrates and rich in protein could result in osteoporosis, due to making the blood “acidic” and leaching minerals from the bones. But this theory has been disproven in several ways.
For example, under normal circumstances the pH of the blood does not change depending on what you eat. Blood pH is tightly controlled within a very narrow range – if it wasn’t, we would die.
Further, the theory that more dietary protein leads to weaker bones has been discredited by clinical trials – people who eat more protein actually tend to have stronger bones. Looking at all available science, higher protein intake hasn’t been shown to harm bone health, and it may even help protect against bone loss in the lower spine.
Finally, repeated studies show no effect on bone density in people eating low carb, even after several years.
Read our complete guide on bone health and low-carb diets.
13. Does low carb cause hair loss?
Occasionally. Temporary hair thinning can occur for many different reasons, including any big dietary change. This is especially common when severely restricting calories (e.g. starvation diets, meal replacements) but it can also occasionally happen on a low-carb diet.
After a period of losing more hair than usual, the lost hairs then grow out again, so that the hair ends up as thick as before.
It’s safe to say that the large majority of people who try a low-carb diet never experience this. Furthermore, it’s likely possible to minimize the risk by not doing a low-carb and low-fat diet at the same time, i.e. by avoiding starvation. Make sure to eat enough fat to feel satisfied and a moderate amount of protein.Learn more about low carb & temporary hair loss
14. Does low carb cause ketoacidosis?
No. Many people mix up ketoacidosis with ketosis.
Ketoacidosis (also known as diabetic ketoacidosis, or DKA) is a rare and dangerous medical condition that mainly occurs in people with type 1 diabetes if they don’t take enough insulin, especially when they are ill.
People with type 2 diabetes who take certain medications (e.g. SGLT-2 inhibitors) can also develop DKA, although this is relatively rare. However, eating a ketogenic diet while taking these medications might potentially increase the risk of DKA.
Also, in rare cases, women eating a very low-carb diet can develop ketoacidosis while breastfeeding.
Ketosis (sometimes referred to as nutritional ketosis), on the other hand, is a 100% natural and safe state for most people.
Nutritional ketosis can be achieved by eating a low-carb diet or by a brief period of fasting.
Being in ketosis usually means that the body is efficiently metabolizing and burning fat, which can be good for weight loss.
15. Do you get a shortage of whole grains on low carb?
Do you need to eat whole grains – like bread or pasta – to stay healthy? While the fiber in whole grains may slow down the absorption of glucose and lower the glycemic index of food (possibly a good thing), it’s less clear what the benefit is on a low-carb diet. There’s likely much less benefit of slowing down the absorption of carbs if you don’t eat many carbs.
Furthermore, there is no high-quality science proving a need to eat whole grains to prevent disease or prolong life. A Cochrane review of high-quality nutrition science found no evidence for that idea.
There’s a widely-held belief that people need to eat grains to get specific nutrients. However, other foods that are lower in carbs are often more nutritious.
Finally, there’s an idea that the microbiome in our guts may benefit from the fiber in whole grains. This is still a controversial topic with a lack of high-quality science. However, there are many other sources of fiber that are far lower in carbs than whole grains.
16. Is salt dangerous for your health?
A low-carb diet is not necessarily higher in salt than other diets. But it’s often recommended to increase salt intake when starting, to reduce the risk of side effects. Many people are concerned about increasing their salt intake — even temporarily — because of longstanding dogma that salt is dangerous.
It turns out that the evidence behind this common piece of health advice is fairly weak. Read more in our comprehensive guide to salt.
Also check out our news post detailing how salt restriction lacks credible evidence
17. Is red meat dangerous?
A low-carb diet is not necessarily higher in red meat than other diets. It’s even possible to eat a vegetarian low-carb diet. However, many people eat a low-carb diet with red meat. Here’s our guide to what the scientific evidence tells us about it:
Low-carb side effects & how to cure them
Common early problems
Later potential issues
Practical low-carb guides
Visual guides