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Low-Carb VS Low-Fat: What The F* Should I Eat?

Is a low-carb or ketogenic diet a miracle cure for obesity? Diabetes? Epilepsy? Or can it increase your risk of heart disease and you should go low-fat instead? If you are utterly confused and overwhelmed by the great diet wars between low-carb vs low-fat fanatics, this guide is for you! Let me help you better understand what is scientifically proven as of today about these two popular diets.

If you have ever tried going on a diet or finally decided to embark on a healthy eating journey, chances are, you came across the great diet wars between low-fat and low-carb (keto) advocates. There’s a lot of online buzz especially about the ketogenic diet lately. Some say it is amazing for weight loss, others warn that it can increase your risk of heart disease. So, what is it? Who should you believe?

If you are tired of figuring out what's the best for you, look no further! In this guide, I'm going to give you a quick rundown on carbs and fats and an unbiased overview on everything you need to know about low-carb vs low-fat diets and their health benefits, according to the most up-to-date scientific research.


What are “carbs” (and are they bad)?

No, carbs aren’t inherently bad (more on this below). To better understand where the confusion lies between low-fat vs low-carb, it's important to clarify what carbs are and the different types of carbs.

Carb is short for carbohydrate. Carbs are one of the three main macronutrients in the diet, and the primary source of energy for all body cells. They are organic molecules typically classified according to their structure based on their level of complexity. There are two types of carbohydrates: simple and complex.

Simple carbs

Simple carbohydrates are made of only one or two sugar molecules. They are typically found in processed foods like white bread and pasta, baked goods (cake, crackers, muffins, cookies etc.), desserts (e.g. flavoured yogurt, ice cream, and candy), cereals and sugary drinks (e.g. sodas, fizzy drinks). These foods are often stripped of their fibre, vitamins, and minerals, so what you end up with is mostly pure sugar.

These simple carbs are, not surprisingly, the least healthy form of carbs. When you ingest simple carbs, they are absorbed quickly and can cause a big “spike” in your blood sugar level, usually followed by an equally big crash. You might feel hungry again quicker, feel sleepy, irritated, sad or tired afterwards. Consuming too much of these have serious consequences on your health: people who tend to eat more sugars have a higher risk of developing diabetes, heart disease, obesity, and dental cavities. If it's not enough, they can also raise blood triglyceride levels, cause bad cholesterol and insulin resistance.

Complex carbs

Complex carbohydrates, which are mostly found in whole plant foods, keep their natural fibre and provide your body with the energy it requires. These carbs take longer for your body to break down, which aids in the regulation of insulin response (and thereby your blood sugar balance), energy levels, and body composition. They are high in fibre, antioxidants, vitamins, minerals, and they provide more satiety.

Complex carbs include starchy vegetables (such as potatoes, sweet potatoes, butternut squash, pumpkin, and parsnips), fruits, and whole grains (e.g. amaranth, barley, brown or wild rice, buckwheat, kamut, millet, oats/steel cut oats, quinoa, spelt, wholewheat bread).


Fibre is part of the complex carbs, but I'm putting it in its own category to emphasise how important it is for our health. Fibre is a type of complex carbohydrate found in all plant-based foods such as legumes, fruit, vegetables, grains and nuts. Fibre, unlike other types of food, is not broken down and absorbed in the small intestine. Instead, it passes through your large intestine undigested. There, it contributes to a healthy gut by feeding our friendly gut bacteria. There is strong evidence that fibre can help reduce your risk of developing bowel cancer, heart disease, stroke, and type 2 diabetes.


What are “fats” (and are they bad)?

Another strong "no" here, but just like carbs, not all fats are created equal.

Most of us have been programmed to believe that fat is bad, but the idea that all fat is bad or that fat in our diet equals fat on our bodies is far from true. Fats are one of the three main macronutrients (protein and carbs are the other two). They are organic molecules made up of carbon and hydrogen elements joined together in long chains called hydrocarbons. These molecules can be constructed in different ways, which creates different types of fats and determines whether fats will be healthy or unhealthy. The three main types of fat: saturated, monounsaturated and polyunsaturated - among which monounsaturated and polyunsaturated fats are the best for us.

Healthy unsaturated fats include nuts and seeds, nut butters, avocados, olives, plant oils (olive oil, avocado oil, flaxseed oil, pumpkin seed oil etc), fatty fish (salmon, sardines, mackerel, anchovies, herring)

Saturated fats should be consumed in moderation, such as coconut milk, chocolate, full-fat dairy products like cream, milk, yogurt, crème fraiche and cheese, grass-fed meat, eggs

There is also an abundance of saturated fats in fast food, fried products, sugary baked goods, and processed meats, which should be avoided completely.

Healthy fats are an important part of our diet as they serve several functions:

  • Fats help the body absorb and use nutrients found in a wide variety of foods, such as the fat-soluble vitamins A, D, K, and E found in fruits and vegetables

  • Fat is the primary component of brain tissue, therefore it's essential for brain function, concentration, memory, and mood

  • The right kind improves heart health

  • Fats keep our metabolism and, in particular, our hormone levels in check

  • Fats provide calories, which makes us feel full after eating

Fats to avoid (at all cost)

Unhealthy fats are typically industrially produced and designed to be non-perishable, such as trans-fatty acids. These trans fats can be found in fried foods like doughnuts, as well as baked goods like cakes, pie crusts, biscuits, frozen pizza, cookies, crackers, margarine and other spreads.

Trans fats raise your bad (LDL) cholesterol while decreasing your good (HDL) cholesterol, and they increase your chances of developing heart disease and type 2 diabetes. Check food labels for words like 'hydrogenated' and 'partially hydrogenated,' - stay away from those!


What is a low-carb or ketogenic diet?

Low-carb diets emphasize eating more protein and fat (typically in form of meat, poultry, fish and eggs) with some non-starchy vegetables. The amount of carbs is heavily reduced, although not eliminated. This means eating less sweets, grains (e.g., bread, pasta, rice), fruits, starchy vegetables, and legumes.

How low the carbs go isn’t set in stone. A typical low-carb diet would recommend no more than 50-150 grams of carbs per day (that’s 200-600 calories per day).

When your body gets under or up to 50g of carbohydrates per day (as a comparison: one medium-sized banana has 27 grams of carbs), you enter the realm of the ketogenic diet. The idea behind the ketogenic diet is to switch your body’s metabolism to an alternative energy source. Normally your body uses glucose (the sugar molecule in carbs) as its main fuel, which is found in many nutritious foods such as fruits, vegetables, legumes, and whole grains. Glucose is the primary source of energy for your tissues and organs like your brain and muscles. But, because your brain is so important to your survival, you do have a “backup” system that activates if your glucose storage is depleted.

That backup energy source is ketones.

Ketones are biochemicals naturally produced by your liver from fat in times of fasting when food is scarce. Your brain, heart, muscle, and kidneys can use them for fuel when you aren’t eating enough carbohydrates. It’s a survival mechanism that switches your metabolism from a glucose-based system to a ketone-based one. That ketone-based metabolic state is called “nutritional ketosis.”

The difference here is that you use the ketogenic diet to switch your metabolism into ketosis without fasting, and this metabolic state continues as long as you strictly maintain this very low level of carbohydrate intake every day.


What is a low-fat diet?

Unlike the keto diet, there is no strict rule or definition to what counts as a low-fat diet. In general, it is recommended to consume 20%-35% of the daily calories from fat, which is about 44 to 77 grams of fat a day if you eat 2,000 calories.

Low-fat diets put an emphasis on eating mostly plant foods (such as vegetables, fruits, nuts and wholegrains) and moderate amounts of lean and low-fat animal-based foods (meat, fish, dairy products, eggs), to help control weight, cholesterol level and overall calorie intake.

Low, but not too low

I mentioned above how fats are essential to many body functions, therefore, it is not recommended to avoid fats completely. Not eating enough fat limits the amount of fat-soluble vitamins A, D, E, and K, as well as essential fats, in our diet. This class of fat-soluble vitamins is critical for vision, skin, the immune system, hormone synthesis, bone health, and the nervous and reproductive systems.

For the best result, reducing the unhealthy saturated and trans fats in our diet and replacing them with healthier unsaturated fats (like the ones listed above) is the most efficient strategy.


The War on Fat & The Rise of the Ketogenic Diet


The low-fat craze began to emerge in 1940s America, the time when scientific studies discovered a link between high-fat diets and high cholesterol levels, implying that a low-fat diet could prevent heart disease in high-risk patients. By the 1960s, the low-fat diet was being promoted not just for high-risk heart patients, but for the entire country. After 1980, the low-fat diet became an overarching ideology supported by doctors, the government, the food industry, and the media, and it slowly became a trend in other markets as well. Many people believed in the low-fat ideology, despite the lack of clear evidence that it prevented heart disease or promoted weight loss. Ironically, during the same decades that the low-fat approach gained such traction and people ate much less fat, another trend emerged that has been classified since then as an epidemic: obesity.

How could that be? Everyone was told that fat is terrible and should be avoided. Low-fat products flooded the supermarkets, so why did people start gaining so much weight? You might have heard or experienced before, but food (namely processed food) tastes pretty bad without any fat added. No fat? Let's just replace it with sugar! Problem solved. With all the low-fat options around, people gorged on foods high in sugar and carbs, and excess amounts of sugar got added into the low-fat products to ensure that their flavour remains highly palatable.

Despite this, the low-fat ideology had such a stronghold that skeptics were dismissed. Evidence of a paradigm shift has only recently begun to emerge, first with the challenge of the low-carbohydrate diet, and then with a more moderate approach reflecting recent scientific knowledge about fats.

Low-carbohydrate diets have grown in popularity in recent years, owing to the so-called "carbohydrate-insulin hypothesis of obesity." This hypothesis proposes that carbohydrates are the primary cause of weight gain.

Things get complicated here because there are both practical and physiological factors at work. For example, going low-carb means limiting your food options, which makes snacking on junk food more difficult. This raises an important point that's worth thinking about: does going low-carb specifically make the difference, or is it more about cutting out the processed unhealthy foods?

Despite a plethora of studies on the effects of low carbohydrate and low-fat diets, there are still important areas that require further investigation.

Let's have a look at what we know about these 2 diets as of today, and how they compare in their effects on our health, weight, cholesterol, blood sugar, and brain function!


Low-fat vs Low-carb for weight loss

A year-long randomized clinical trial (DIETFITS) discovered that a low-fat diet and a low-carb diet resulted in comparable weight loss and improvements in metabolic health markers. Furthermore, neither insulin production nor the genes tested had any effect on predicting weight loss success or failure.

For weight loss, there is no such thing as the "best diet" - neither a low-fat nor a low-carb diet is inherently better. The current evidence suggests that the only factor in weight loss is consuming less calories than one needs, regardless of the makeup of protein, fat, and carbohydrates. So, it doesn't matter if you eat carbs or fats - as long as you are in a calorie deficit, you will lose weight.

As both of these diets can help, the one that works best for you is one that you can stick to.


Low-fat vs Low-carb for cholesterol

The ketogenic diet may increase blood LDL cholesterol (the bad cholesterol), especially if it includes high levels of saturated fats like coconut or palm oils, lard, butter, processed meats (sausage, burgers, bacon, salami, etc.), cakes, biscuits, pre-packaged processed foods and so on. Apart from saturated fat, the lower fibre intake might contribute to this effect as well.

As a consequence, total cholesterol also tends to be more elevated on a ketogenic diet than on a low-fat diet. This effect appears to persist on average in the long-term trials that have been conducted so far. Although your body needs cholesterol to build healthy cells, high levels of cholesterol (especially high LDL) can increase your risk of heart and circulatory diseases like heart attack, stroke and vascular dementia.


Low-fat vs Low-carb for blood sugar

When compared to various other control diets in both short and long-term trials, a keto diet has been shown to reduce fasting blood glucose regardless of weight loss compared to low-fat diets, especially in those who already have elevated levels.

This can be explained quite simply. When we eat a carb-rich meal, the carbohydrates get broken down into glucose, the sugar our body uses for fuel. Glucose is absorbed through the walls of the intestine into the blood. The pancreas produces insulin to help glucose enter the cells - insulin can basically knock on the cell's door and as a messenger, it can tell the cell that glucose is available if energy is needed. The cell then can take in the glucose molecule from the blood and burn it as fuel, essentially bringing the blood sugar level down (as glucose is getting stored up in the cells). When we keep eating a diet full of simple carbs, our body needs to deal with continuous blood sugar surges, forcing the pancreas to constantly release large amount of insulin. Eventually, the insulin receptors of the cells become less and less responsive to allow glucose to enter, leading to even more insulin secretion as the pancreas is trying to control the increased blood sugar levels – this is known as insulin resistance, which can develop over years and can remain undiagnosed for a long time. Insulin resistance is a precursor of hyperinsulinemia and type 2 diabetes, in which cases your body is unable to metabolise sugar (not responding to insulin) which causes the blood sugar to remain high at all times, damaging various organs.

No glucose = no insulin needed, which is why a keto diet can be beneficial to control blood sugar.

Now, there is an argument that debates the role of carbs in insulin resistance and diabetes, and some interesting research is ongoing about the role of fats. According to this view, taking out the carbs from the diet and switching to high fat is only a temporary and superficial solution, as it treats the symptom, but not the root cause. Increased consumption of fat causes fat to build up inside muscle cells where it does not belong (also known as intramuscular fat). Eventually, the accumulated fat starts blocking the insulin message from getting through, and therefore, cells are unable to take in glucose as they should. Once fat is clogging the pathway, the blood glucose (sugar) will rise again. In summary, to fix the root cause of blood sugar imbalances, fat must be cleaned out of the cells. This argument can be supported by the fact that foods including vegetables, fruits, beans, lentils, and whole grains, have been linked to lower diabetes risk, although all of them are very limited on a low-carb/ketogenic diet.

At the moment, however, there is no definitive consensus on the best diet for blood sugar imbalances and diabetes. Research on low-carb diets seems to confirm that low carbohydrate diets may be more effective for managing type 2 diabetes than low-fat diets, but there are still questions unanswered. It is also not clear whether the effects of low-carb diets are due to the diet itself or secondary to the weight loss they may cause.

A systematic review of 10 studies suggested that the Mediterranean diet (consisting of whole grains, fruits, vegetables, seafood, beans, and healthy fats) is probably the most effective dietary approach to improve blood sugar control, compared to low-carb or low-fat diets. However, this review included a very small number of studies that had many differences in population characteristics, so further research is needed for sufficient evidence.


Low-fat vs Low-carb for brain health

There is little evidence that a ketogenic diet improves cognitive function in healthy people. Many of the recent studies have lacked proper dietary control and have not used reliable methods to ensure ketosis was achieved. Overall, these studies appear to suggest that cognitive function and mood may be negatively impacted during adaptation to a ketogenic diet over a one to three week period, but that once the body adapts, ketosis has no negative impact on cognitive function. Improvements in cognition previously reported may be indirect benefits of weight loss and/or other metabolic improvements in obese or overweight individuals. More high-quality research is required in this field.

When it comes to specific conditions, the ketogenic diet has some promise in epilepsy, dementia (Alzheimer’s), ALS (amyotrophic lateral sclerosis), and traumatic brain injury.


And the winner is...

... whatever you can sustain with the highest quality of real food. Probably not what you wanted to hear and this might be a disappointing answer to you, but there is no definitive "good" diet that works for everyone. The best approach for you will depend on your individual life circumstances and health conditions.

You should base your diet on personal preferences, health goals, and long-term sustainability. Studies show the overall quality of a food or diet is more important than focusing on just one nutrient, like carbs or fats.

According to Harvard Health, “The best diet is the one we can maintain for life and is only one piece of a healthy lifestyle. People should aim to eat high-quality, nutritious whole foods, mostly plants (fruits and veggies), and avoid flours, sugars, trans fats, and processed foods (anything in a box).”

A solid foundation for any diet should be:

  1. More whole foods

  2. More plants (fruits and veg)

  3. Less added sugar

  4. Less refined grains

Those are four points agreed on by champions of every type of diet I can think of — vegan, paleo, low-fat, low-carb, Mediterranean, etc.


Risk factors to consider

Low-carb/ketogenic diets heavily limit fruits, starchy vegetables, whole grains, and legumes (beans, lentils, and split peas). As a result, they can be deficient in nutrients found in these foods, including thiamine, folate, vitamin A, vitamin E, vitamin B6, calcium, magnesium, iron, and potassium. This can lead to health problems and long-term concerns like bone loss, gut problems, and chronic diseases.

Same goes for restricting fats - as mentioned above, fat is needed for the absorption of fat-soluble vitamins A, D, E, and K, as well as many other functions in the body. Not eating enough healthy fats can cause nutrient deficiencies and can lead to serious issues in hormone synthesis, immune system, nervous and reproductive systems.

There are additional cautions for those with diabetes and anyone taking medications for blood sugar control. See your doctor about adjusting your medications before starting a ketogenic diet as there is a risk of severe low blood sugar.

The ketogenic diet is not recommended if you have pancreatitis, liver failure, disorders of fat metabolism, carnitine deficiencies, porphyria, or pyruvate kinase deficiency. If you’re on a ketogenic diet, it’s recommended that your kidney function is regularly monitored by your healthcare professional.

As low-carb diets are restrictive and may not provide all necessary nutrients, this diet isn’t recommended for adolescents or pregnant or breastfeeding women.

It's important to remember that most of the research on low-carb diets is short-term - we don’t know all the possible health effects over the course of many months or years.


Bottom Line

Instead of experimenting on yourself, I highly recommend that you see a health professional before embarking on any diet. This can save you significant time, money and disappointment, and ensure that you get the right foods and nutrients to thrive and achieve your goals.

Changing your diet to reach health goals is something I specialize in! If you’re considering starting a low-carb, low-fat diet or you are simply not sure what works for you, book an appointment with me and let's discuss how I can help you.


Sources & Further Reading

Lydia A. Bazzano, MD, PhD, MPH*, Tian Hu, MD, MS*, Kristi Reynolds, PhD, Lu Yao, MD, MS, Calynn Bunol, MS, RD, LDN, Yanxi Liu, MS, Chung-Shiuan Chen, MS, Michael J. Klag, MD, MPH, Paul K. Whelton, MD, MSc, MB, Jiang He, MD, PhD (2014). Effects of Low-Carbohydrate and Low-Fat Diets

A Randomized Trial. Retrieved from

Examine. (2018, February 20). Does “low-carb” have an official definition? Retrieved from

Examine. (2018, February 20). Deep Dive: Cutting carbs may help reverse diabetes, but dietary adherence remains a challenge. Retrieved from

Harvard Health. (2018, April 9). Which diet is best for long-term weight loss? Retrieved from

Harvard Health. (2018, November). Both high-carb and low-carb diets may be harmful to health. Retrieved from

Harvard Health. (n.d.). Low fat, low carb, or Mediterranean: which diet is right for you? Retrieved from

Harvard Health. (n.d.). Going low-carb? Pick the right proteins. Retrieved from

Medline Plus. (2018, January). Carbohydrates. Retrieved from

StatPearls [Internet]. (2019). Physiology, Carbohydrates. Retrieved from

Harvard Health Publishing. (2018, October). Should you try the keto diet? Retrieved from

Harvard Health Publishing. (2019, August). Can the keto diet help me lose weight? Retrieved from

Masood, W. & Uppaluri, K. R. (2019, March 21). Ketogenic Diet. Retrieved from

Shilpa, J., & Mohan, V. (2018). Ketogenic diets: Boon or bane?. The Indian journal of medical research, 148(3), 251–253. doi:10.4103/ijmr.IJMR_1666_18

U.S. Department of Health and Human Services and U.S. Department of Agriculture. Office of Disease Prevention and Health Promotion. (2015, December). Dietary Guidelines for Americans 2015-2020, Eighth Edition. Retrieved from

Barnard RJ, Lattimore L, Holly RG, Cherny S, Pritikin N. Response of non-insulin-dependent diabetic patients to an intensive program of diet and exercise. Diabetes Care. 1982;5:370-374

Barnard RJ, Massey MR, Cherny S, O’Brien LT, Pritikin N. Long-term use of a high-complex-carbohydrate, high-fiber, low-fat diet and exercise in the treatment of NIDDM patients. Diabetes Care. 1983;6:268-273


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