The 3 main macronutrients that are relatable to a keto diet are fats, proteins, and carbohydrates. All three of these nutrients have different effects on ketosis from their digestion and have consequent effects on blood glucose and hormones.
- Fats are 90% ketogenic and 10% anti-ketogenic, due to the small amount of glucose that is released in the conversion of triglycerides.
- Proteins are typically ranged at 45% ketogenic and 58% anti-ketogenic since insulin levels rise from over half of the ingested protein being converted to glucose.
- Carbohydrates are of course 100% anti-ketogenic, as they raise both blood glucose and insulin.
Protein and carbohydrates will impact our bodies from transitioning into ketosis, but the most important thing to understand is how these nutrients are being utilized for energy. This is through our metabolic pathways after we have ingested nutrients.
Well you might be asking yourself what the heck metabolic pathways are. It’s pretty much the way our bodies handle the breakdown of fats, proteins, and carbohydrates and how it utilizes those depending on the current “state” of our body.
There are 3 different states that we can be in:
- Fed – Right after a complete meal.
- Fasting – haven’t eaten in 2-8 hours.
- Starved – haven’t eaten in more than 48 hours.
In the fed state, the main nutrients are broken down in separate metabolic pathways:
- Fats go straight to the liver to be broken down into fatty acids and glycerol. They are then sent around the body to repair cells and make different chemicals/tissues in the body. Excess fats are stored as triglycerides in the fat cells.
- Proteins are processed into amino acids through transamination and sent off to create neurotransmitters, non-essential amino acids, and other protein based compounds in our body. If we have any extra amino acids, they circulate and repair tissue or get stored as glucose.
- Carbohydrates are broken down into glucose which is used as immediate energy. The spike in glucose levels will trigger insulin release, which then helps store the glucose as either glycogen or fat in our cells.
The fasting state happens when our blood glucose is at borderline level, which also means our insulin levels are decreased. With the drop in blood glucose, another hormone called glucagon is released to harness the processing of fuel from storage.
In a fasting state, our nutrients are broken down by different processes, but they are all metabolized the same way. They are all broken down into acetyl-CoA, which is an important part of creating ATP (an energy molecule) in the Kreb’s Cycle.
- Liver glycogen is released and glucose levels increase in the bloodstream. In turn, this glucose is primarily used by the brain and red blood cells.
- Free fatty acids are released from the fat cells that are in the form of triglycerides. These are the main fuel source for the liver and muscles while we are sleeping. The liver will also form ketones from these, and we can use them as fuel if needed. More triglycerides are broken down and released if we are in a fasting state for longer.
Once we have been in a fasting state for longer than 48 hours, we transition into a starved state. The glycogen in our muscles and liver will run out. The liver will begin to break down lactate in order to create more glucose to fuel our red blood cells.
- The liver begins production of ketones which enter the blood steam, and the brain and muscles begin to use them as fuel through oxidization.
How does this all relate back to the keto diet? With the lack of glucose in our systems, our body is essentially mimicking a starved state. The liver creates more ketones to use as energy, as there is less glucose available – so we are using more of our fats as energy.
Protein is vitally important in a ketogenic diet, but it’s also a tricky nutrient. If we don’t eat enough protein, we lose muscle mass. You might be thinking “well I can just eat all the meat I can to overdose on the stuff”. Well, that would be pretty delightful, but the massive amounts of proteins would raise the glucose levels in our blood steam.
As you saw, protein is 46% ketogenic and 54% anti-ketogenic, meaning that too much of the stuff will knock us out of ketosis. We have to fall between narrow ranges in our protein intake: enough to not lose muscle mass, but not too much to knock us out of ketosis.
This narrow range is quite hard to determine, as it differs from person to person. Some have reported trouble maintaining keto if they eat excessive protein in a single day, or if they eat too much protein in 1 sitting. Others have 1.2g of protein per pound of body weight and have no problems transitioning and staying in ketosis.
This may also be in relation to the amount of exercise you do, as glycogen depletion will allow carbohydrates to be used up quicker. That being the case, the suggested protein intake depends on your lean body mass and what your activity levels are like.
- Sedentary: 0.8g of protein per pound of lean body mass.
- Lightly Active: 0.8 – 1.0g of protein per pound of lean body mass.
- Highly Active: 1.0 – 1.2g of protein per pound of lean body mass.
Even though the ketogenic diet is known for the high amounts of fat eaten, dietary fats have a pretty minimal effect on ketosis. In the end, fat intake will determine how much body fat is being used for fuel.
Since fats are 90% ketogenic and only 10% anti-ketogenic, we can get away with big amounts of fat intake. Yes, the glycerol from triglycerides produce glucose, but think of it in terms of the amount of grams you eat. If you eat, say, 160g of fats in 1 day – that is only 16g of glucose.
Since fats are mostly consumed over the entire day and not just in 1 sitting, your body will be using that glucose without you even noticing it’s there. The only time in the day we deviate from a consistent fat intake is after a workout. Fats slow down the digestion process and will slow the absorption of the protein you intake after your workout, so they’re generally not recommended.
As one of the most restricted nutrients on a ketogenic diet, the carbohydrate has the biggest effect on ketosis. The general rule is to consume no more than 30g of carbs a day if on an SKD.
As carbohydrates are processed, they are converted almost gram to gram into glucose when entering the bloodstream. Here, the glucose really has a number of different things that it can do. It will either be burned up immediately for fuel, stored as glycogen in the muscles or liver, or if excess carbohydrates are consumed, it will be stored into fat cells.