High carbohydrate diets are evil…but your brain needs them…but they make you fat and sick…but the Food Guide says to eat plenty of them!
I’m sure you’ve heard this argument before. Funny enough, one of the only things the conventional and holistic health community can agree on is not having a consistent answer about carbohydrates. Is it low carbohydrate, high carbohydrate, or something in the middle? To answer these questions let’s look at the scientific evidence and review the diets of populations free of modern diseases.
Low Carbohydrate vs Ketogenic Diets
Believe it or not, carbohydrates are not on the list of essential human nutrient. In their absence our bodies create ketones from fat, which enter our energy pathways similar to glucose (1). In fact, most of our brain cells can use ketones for energy and ketones are arguably more metabolically efficient than glucose, producing less oxidative stress and inflammation (2, 3). However, our brains do need about 50 grams per day of glucose to function optimally but that amount can be supplied through gluconeogenesis, creating glucose from fat and protein (2).
Consuming 50 grams or less of carbohydrates per day is a ketogenic diet and has a physiological response as outlined above, but it’s also important to understand that there is a scale of carbohydrate intake from ketogenic to very high carbohydrate.
- Ketogenic = 50 grams or less.
- Low carbohydrate = 50 – 100 grams.
- Moderate carbohydrate = 100 – 200 grams
- High carbohydrate = 200 – 250 grams
- Standard North American Diet = 250 grams or more
As you move up the carbohydrate intake scale your body will rely increasingly less on ketones and gluconeogenesis.
Benefits of Low Carbohydrate Diets
There is no shortage of evidence for the benefits of lower carbohydrate diets. Compared to common low fat, high carbohydrate diets ketogenic diets are effective interventions for weight loss, cardiovascular disease, metabolic syndrome, diabetes, neurodegenerative diseases, traumatic brain injury, epilepsy, polycystic ovarian syndrome, and some cancers (3, 4, 5). Furthermore, ketogenic diets reduce systemic inflammation, chronic pain, and can improve athletic performance (2, 6, 7).
Similar to ketogenic diets, low carbohydrate diets are also effective interventions for weight loss, cardiovascular disease, metabolic syndrome, diabetes, sub-clinical inflammation, and improving athletic performance (7, 8, 9, 10).
Additionally, these benefits are seen in the absence of caloric restriction meaning people are more satisfied, can maintain the diet, and have improved quality of life I comparison to low calorie or low fat diets (11).
Drawbacks of Low Carbohydrate Diets
Two common arguments against low carbohydrate diets are that they are high in fat and protein. Fortunately, a whole food, low carbohydrate diet would not include bad fats (trans and excess Omega 6), and reliable evidence indicates that saturated fat is good for us (13, 14). A low carbohydrate diet does not need to contain excessive protein and even at the high end of protein intake (30% of calories), and the absence of existing kidney problems, there is no evidence of negative impacts on kidney function (3). In reality, there is little to no risk associated with low carbohydrate diets; however, the closer the diet becomes to ketogenic some risk can occur.
Dietary carbohydrate content impacts the metabolism of thyroid hormones because insulin is required in this process (15). However, there is no clear evidence that ketogenic diets negatively impact thyroid function yet many practitioners indicate some patients experience reduced thyroid function with long term ketogenic diets. Another concern is that ketogenic diets can increase the stress hormone cortisol, leading to a dysregulated hypothalamic-pituitary-adrenal system, otherwise known as adrenal fatigue (16).
Healthy gut bacteria live off the fibre we cannot digest and there is some evidence to suggest that very low carbohydrate diets can have a negative impact on gut bacteria, reducing number and diversity (17). These effects may be positive in the short term for pathogenic bacterial overgrowth, but could be detrimental over a longer period of time.
Ketogenic diets can have a positive effect on endurance and short anaerobic (<10 seconds) performance; however, the evidence is mixed for longer anaerobic durations such as interval training, hockey, CrossFit, etc. This is because longer anaerobic activity relies more on muscle glycogen which is reduced in the presence of a ketogenic diet (2, 18).
Malnutrition is a viable concern depending on how a ketogenic diet is implemented. If vegetables and fruits are fully removed and the focus is on processed low carbohydrate foods (protein bars) versus whole foods (meat, fish, etc.) there will undoubtedly be a level of vitamin and mineral deficiency.
However, aside from some risk associated with long term ketogenic diets, the evidence is clear that a whole food diet with carbohydrate content between a Standard North American and ketogenic diet is beneficial (19, 20, 21).
Quality vs Quantity
Regarding carbohydrate quality, one thing we know is low glycemic load diets are very beneficial for health and further clarity can be gained by reviewing the diets of populations who experience no modern disease (22). Surprisingly, these groups experience robust health on a wide range of carbohydrate intakes. For instance, the Masai exclusively eat milk and meat while the Tokelu eat a high fat moderate carbohydrate diet (23, 24); while on the other hand, the Kitavan and Okinawa diets are 70-85% carbohydrate, yet the occurrence of modern diseases is absent (25, 26). However, what differentiates these populations from modern diets is their carbohydrates come exclusively from whole foods, mainly fruits and tubers.
Carbohydrate Take Away
Clearly, both carbohydrate quality and quantity are important factors and there is no one size fits all approach for carbohydrate intake. Those who are overweight, have metabolic syndrome, diabetes, neurodegeneration, epilepsy, arthritis, other inflammatory diseases, polycystic ovarian disease, or brain injury may consider ketogenic and low carbohydrate diets, while athletes and those who generally feel better eating more carbohydrates could fall anywhere from low to high carbohydrate intake. Some people even feel better with strategic carbohydrate intake timing (ie. eating carbs only after a workout) or cyclic ketogenic diets, which may more closely match our ancestral eating patterns. Ultimately, the key is self-experimentation with one connecting factor: it must be a whole food diet with the majority of carbohydrates coming from fruit and starchy tubers.