Low Carb Myths

There are many myths, misconceptions and concerns around low carbohydrate high fat (LCHF) or ketogenic diets. Let’s delve into each and see whether they’re trumped up or if there’s any truth behind the charges.

MYTH#1: LCHF raises cholesterol and heart disease risk

Perhaps the greatest concern is that an LCHF diet raises LDL cholesterol, also thought of as “bad cholesterol”, and total cholesterol. The lipid hypothesis postulated that this rise in total and LDL cholesterol leads to increased cholesterol build-up (plaques) in blood vessel walls (a process called atherosclerosis), which in turn increases your chance of getting and dying from heart disease. Indeed LCHF is often, but not always, associated with an increase in total and LDL cholesterol concentrations. However, this does NOT translate to an increased risk of blood vessel plaque build up, nor chances of getting or dying from heart disease. In fact, people with higher LDL cholesterol are at no higher risk of dying from heart disease than those with lower LDL cholesterol. And lowering LDL cholesterol with statin medication does NOT reduce your risk of dying from heart disease. Clearly LDL cholesterol has had a bad rap and isn’t the black sheep of the cholesterol family after all. 

While LDL cholesterol is found in arterial plaques, it only ends up there when it’s damaged (in the context of things like high free radicals (oxidants) and blood sugar). It’s those damages of LDL cholesterol that increase heart disease risk, rather than the amount of circulating LDL cholesterol. When LDL cholesterol is raised it is likely that way in order to perform very important functions – e.g. fighting inflammation or fixing things – or it may be a marker (rather than a cause) of something wrong (e.g. low vitamin D production). High triglycerides (fats in the blood) are a far better indicator of heart disease risk, particularly when HDL (so-called “good”) cholesterol is low. An LCHF diet is really good at lowering triglycerides and raising HDL cholesterol – indicating a lowered chance of getting and dying from heart disease.


MYTH#2: Salt raises blood pressure and should be reduced in the diet

Most of us were brought up thinking that fat isn’t the only heart disease culprit… salt is too. The concern around salt is that it raises blood pressure. So reducing dietary salt intake is thought to reduce your risk of heart failure caused by high blood pressure. However, studies now indicate that only certain people, under certain conditions are salt sensitive – meaning that their blood pressure increases in response to higher dietary salt intake. Those conditions appear to be 1.) high sugar or refined carbohydrate intake and 2.) low potassium (and other minerals – magnesium and calcium) intake. When dietary sugar is eliminated, carbohydrates reduced and potassium intake is sufficient, salt loses its blood-pressure-raising ability in salt sensitive people.

An LCHF or keto diet is naturally low in sugar and carbohydrates and higher in potassium (from plenty of non-starchy veg). As such, in the context of an LCHF diet salt intake is extremely unlikely to raise blood pressure, even in salt-sensitive people.


MYTH#3: LCHF/keto does not supply sufficient fibre to meet recommendations

A study by Dr Caryn Zinn and colleagues, published in the British Medical journal, clearly dispels assertions that an LCHF diet can’t meet dietary fibre recommendations. So that’s the end of that argument. But wait, there’s more… The benefits associated with fibre may be even more apparent in those following a ketogenic diet. Fibre’s health benefits appear to be largely attributable to fibre’s conversion into the short chain fatty acid butyrate by bacteria in the large intestine (aka colon). A ketogenic diet, even one devoid of fibre, creates plenty of butyrate (aka butyric acid or beta hydroxybutyrate, which is a ketone) – even more than is created by gut bacterial fermentation of dietary fibre. So the benefits of fibre may be very contextual. It may be beneficial in the context of a conventional diet, where you’re not having the benefits of higher circulating butyrate. On the other hand, when you’re on a low carb, ketogenic diet fibre’s benefits may be relatively superfluous



MYTH#3: There are insufficient nutrients in a low carb diet

This assertion comes from observations about the nutrient composition of classic ketogenic diets used to control paediatric epilepsy. This version of keto is far more restrictive than ketogenic diets not used to treat paediatric epilepsy, such as those used to treat metabolic syndrome, diabetes, cancer, Alzheimer’s, or to promote optimal health. The latter are far less restrictive and evidence indicates they can be nutritionally sufficient. That’s because, unlike ketogenic diets for paediatric epilepsy, keto diets used for health in adults don’t restrict animal foods or protein. Animal foods are very rich in bioavailable nutrients. Recommendations for nutrient intakes to ensure people are getting enough, are based on nutrient intakes required in people eating conventional diets heavy in plant-based foods. Nutrients in plant foods appear in forms that are less easily absorbed and used by the body (i.e. less bioavailable). Additionally, plant foods contain anti nutrients (e.g. lectins, phytates, oxalates, wheat germ agglutinin) which bind to nutrients, inhibiting their absorption. As such, people can likely meet nutrient recommendations more easily with lower nutrient intake levels if they get them from animal sources. In other words animal-based nutrients have more bang-for-buck than plant-based nutrients. 

Dr Caryn Zinn’s study showed that LCHF diets can indeed meet recommendations for all nutrients, except possibly for iron in reproductive age females. However, iron from animal sources is very bioavailable, so you would likely need less iron than if you were getting iron in it’s less absorbable plant form.


MYTH#4 Ketosis is dangerous

This comes from the observation that increases in ketone levels in Type 1 Diabetes and very uncontrolled advanced Type 2 Diabetes result in a ketotic coma. In these cases, blood ketone concentrations rise to toxically high concentrations, known as ketoacidosis (defined as over 5, generally over 10, often over 20 mmol/L). Toxic concentrations of ketones can result in coma and even death. However, remember the old adage, “the dose makes the poison”? In high enough doses anything can be toxic. Even water. If you drink more than 6L of water at one time you can die. But we all know that water isn’t toxic. In fact, it’s healthy and necessary to sustain life. Similarly, ketones are not toxic in and of themselves. It’s the dose that makes the poison. Most people’s bodies’ won’t allow their ketones to rise to toxic levels. The hormone insulin, even at very low concentrations, keeps ketones in check. Generally, only people who don’t have any insulin or can’t make enough insulin (i.e. type 1 or advanced type 2 diabetics) can achieve toxic, ketoacidotic concentrations of ketones. Ketones, produced during fasting, ketogenic diets, exercise, or in infants at birth and during exclusive breastfeeding, are known as part of nutritional ketosis (not ketoacidosis), a normal metabolic state. Nutritional ketosis is when blood ketone concentrations are 0.3-3 mmol/L (though some people say that even ketone levels of below 5 or possibly even up to 10 may be safe provided it’s not in a diabetic). Low carbohydrate ketogenic diets produce a healthy state of nutritional ketosis, not a toxic state of ketoacidosis.


MYTH#5 A LCHF diet is bad for the kidneys

Claims that LCHF diets impair kidney function, are based on concerns over excessive protein consumption, due to the misconception that LCHF is a high protein diet LCHF is actually moderate in protein, well within normal protein recommended intake ranges of 15-35% of total daily energy intake and below 2.2 g of protein per kilogram ideal body. Hypothetically, even if an LCHF diet were high in protein there would still be insufficient evidence to indicate that a high protein intake is bad for the kidneys unless you have pre-existing kidney disease. As kidney disease prevents you from processing and excreting metabolites of protein properly. So in the context of preexisting kidney disease you would indeed not want a high protein diet. But, a higher protein diet in the context of healthy kidneys does not appear to be a problem.


There are also concerns that a ketogenic diet may cause kidney stones. This is because kidney stones form in 3–7% of children on the Classical classical ketogenic diet, used for paediatric epilepsy to control seizures (Phillips, 2018). Kidney stones associated with ketogenic diets used for paediatric epilepsy are due to dehydration and acidic urine (causing urate crystal formation). They can be prevented with oral citrates, which alkalize the acidic urine. Kidney stones are less of a problem (or possibly not a problem at all) for adults following a ketogenic diet (Martin-McGill et al, 2017). Adults on ketogenic diets have fewer and/or only minor adverse effects associated with ketogenic diets in general, compared to children (Allen et al, 2014). Most side effects associated with a ketogenic diet in adults result from the natriuresis of ‘fasting’ (i.e. flushing out of sodium (salt) and fluid) and associated dehydration. This dehydration can easily be prevented with sufficient sodium (salt) and fluid replacement – likely the same goes for prevention of kidney stones caused by dehydration.


MYTH#6 An LCHF diet makes bones weak

Again, this assertion is based on the misconception that LCHF is a high protein diet. High protein diets are thought to acidify the blood, which leaches calcium from the bone into the blood, from where it then gets excreted by the kidneys in the urine. This theory came from the observation that people who eat higher protein diets (even within the upper normal range) excrete more calcium in the urine. So, this leads to the conclusion that this calcium was being leached from the bone, which would cause increased bone loss and reduced bone mineral density (strength). Firstly, remember that LCHF isn’t high in protein. However, it can be higher in protein than other diets, depending on how you follow it. So, should you worry about your bones? Luckily not. Even when more calcium appears in the urine, studies indicate that it doesn’t come from the bone after all. It appears that when eating a higher protein diet, more calcium is absorbed, and the excess is excreted out in the urine.


MYTH#7: LCHF increases gallstone formation

Indeed, if you already have gallstones or bile sludge in your gallbladder, an LCHF diet will flush these out and, during exit, they may get stuck in the bile duct, precipitating a gall stone “attack”. However, an LCHF diet isn’t responsible for the formation of these gallstones in the first place. It’s merely responsible for getting them moving by increasing bile throughput, which actually reduces your chances of making more gall stones in the long run.  Here’s how it works…

The gallbladder is a little storage pouch where bile that’s made by the liver awaits it’s release into the gut when there’s a job to be done. Bile’s job is to dissolve dietary fat that enters the gut, much like dishwashing soap dissolves layers of fat left on your plate into smaller droplets. These fat droplets are now just the right size for digestive enzymes to break apart into fatty acids which can be absorbed into the bloodstream. So when you eat fat, bile gets released from the gallbladder so that fat can be dissolved, digested, and absorbed. If you eat a low fat diet then the bile sits in the gallbladder for a longer period, where it gets concentrated and turns into bile sludge and eventually can turn into gall stones. If you then adopt a high fat diet, the liver makes more fresh bile to meet the demand for fat digestion. The old bile sludge or stones need to move out to make way for the fresh bile. They can get stuck in the small pipe leading from the gallbladder to the gut, resulting in a gallstone attack. Keeping the bile fresh and flowing, but eating an LCHF diet is a great way to prevent future gallstones.


MYTH#8: LCHF increases your risk of gout flare-ups

When you are eating a ketogenic diet then you are producing more ketones (aka. ketone acids). In the first few weeks of following a ketogenic diet your body is still adapting to using these ketone acids, so you urinate quite a lot of them out. Only after about 3 weeks, does your body stop excreting them and start using them properly for energy. If you already have gout then you have high uric acid levels. Acids complete for excretion at the level of the kidneys. So, if you have preexisting gout, one would expect that during the first few weeks of keto, ketone acids and uric acids would compete for excretion in the kidneys. This would be expected to result in less excretion of uric acid, increased uric acid concentrations in the blood, increased uric acid precipitation and urate crystals building up in the joints, resulting in gout attacks. 

However, in practice, there is no indication of increased gout flare ups in people with pre-existing gout who follow a ketogenic diet (based on clinical trials). Just to be safe though, if you have gout and plan on adopting a ketogenic diet, be sure to check-in with your doctor and have medication on hand in case of a flare-up.

Luckily, following a ketogenic diet may help prevent you from getting gout in the first place.


MYTH#9: Hypothyroidism

There is concern that LCHF may aggravate hypothyroidism or even precipitate it. This is because LCHF is associated with lower concentration of T3. However, despite low T3 levels there is no evidence of increased symptoms of hypothyroidism when following an LCHF diet. This could be because on an LCHF diet, the body becomes more sensitive to thyroid hormone’s effects.


Myths and misconceptions abound around LCHF and ketogenic diets. Now you know where they come from and what to make of them.

About the Author

Tamzyn Murphy is a registered dietitian and researcher, with a Masters degree in Physiology with distinction, in which she investigated low carbohydrate high fat (LCHF) diets in Type 2 Diabetes. She is also a Nutrition Network lecturer, researcher and writer. Tamzyn’s early work experience as a dietitian in the community sparked her passion for debunking the myths surrounding diet in the quest to find a nutritional therapy that can prevent and reverse the rising epidemics of obesity and related diseases. After her time in the community, Tamzyn worked in nutritional supplement research and development, and as a nutrition editor and writer for a health magazine. While researching articles for the health magazine Tamzyn became aware of the benefits of LCHF diets. This prompted Tamzyn to pursue her Masters degree and research into LCHF diets, and to become co-founder of Real Food Dietitians, a private dietetics practice focusing on LCHF diets. 

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