Mechanics of the Ketogenic Diet
Boiled down to its most basic level, the ketogenic diet is very simple—eat fewer than 50 grams of carbohydrates daily, eat 1.2 to 1.5 grams of protein per kilogram of body weight, and fill in the rest with fat. If you do that, after a few days your body will start relying on fat oxidation and ketone bodies for fuel. Of course, as with all things nutrition, the nuts and bolts are a little more complicated than that. For optimal health, there are considerations other than macronutrient composition.
Because of the late Dr. Robert Atkins and his “diet revolution” that was originally popularized in the early to mid-1970s, the ketogenic diet often comes to mind as the type of short-term diet used for weight-loss purposes. Although this is not what Dr. Atkins intended or advocated for, it is still the net result of his promotion of the ketogenic diet. While a ketogenic diet will almost certainly result in weight loss relatively quickly, it has the potential to be much more than a means to a temporary weight-loss end. I say temporary because if you use the ketogenic diet for weight loss but immediately return to a high-carbohydrate diet, you will most likely gain back any weight you lost as your body again has to deal with the excessive amount of glucose it receives.
The benefits of a ketogenic diet extend beyond weight loss. For example, the medical community has used the ketogenic diet to effectively control epilepsy since the 1920s, when the diet was developed as an alternative to fasting. There are several theories regarding how the ketogenic diet is able to prevent epileptic seizures but there is not currently a consensus. Most likely it has to do with the brain’s fuel shift from glucose to fatty acids and ketones.
Recently there has been an explosion of interest in the ketogenic diet’s potential uses beyond weight loss and the control of medicinally intractable epilepsy. The ketogenic diet looks to have promising applications for the treatment of a variety of neurological disorders including amyotrophic lateral sclerosis (ALS), multiple sclerosis (MS), Alzheimer’s disease, dementia, Parkinson’s disease, chronic migraines, and even stroke recovery. It makes perfect sense that the ketogenic diet could provide relief for individuals with these conditions because one of the primary effects of ketosis is a shift in neurologic fuel source, as the common thread between many neurological disorders is some form of glucose metabolism malfunction.
What Is the Ketogenic Diet?
The ketogenic diet is awesome.
OK, more in depth: The ketogenic diet is a dietary pattern that shifts your metabolism from relying on glucose as its primary fuel source to relying on fat. This shift is likely an evolutionary trick that humans developed to account for periods in which quick energy was not available and we needed to rely on fat storage to prevent starvation. Almost all of the cells in the body can oxidize, or break down, fat and utilize ketone bodies for fuel instead of the typically preferred glucose. The few cells that do require glucose, including red blood cells (RBC) and certain portions of the brain, can have their needs met by the conversion of protein to glucose.
Even in very lean individuals, the body has a greater capacity to store fat than carbohydrates. The adaptation to burn fat as fuel would have allowed our ancestors to survive the periods in which food was harder to come by.
Typically, your body can store about 2,000 calories of carbohydrate at any given time. Those calories are then converted and stored as about 400 grams of glycogen, which is the stored form of glucose, in skeletal muscle. Muscle glycogen cannot be used by other parts of the body; 100 grams of glycogen stored in the liver can be distributed throughout the body; and 25 grams of glucose circulate in the bloodstream. By contrast, energy stored as fat can easily exceed 10,000 calories, even in lean individuals, and would obviously be of much greater use in those with excess body fat.
Simple arithmetic shows us why a body utilizing fat for its fuel source would be able to keep going much longer than one relying on glucose and glycogen stores. It is for this long-term fuel adaptation that more and more endurance athletes, like ultra-marathon runners and long-distance cyclists, are turning to the ketogenic diet to give them a competitive edge over those that rely on carbohydrate metabolism and must refuel several times during a race.
What Does the Ketogenic Diet Do to the Body?
The ketogenic diet has many physiological effects of great importance. The most obvious effect of the ketogenic diet is in its name—it initiates the production of ketones. Ketones, or ketone bodies, are molecules that are produced during the breakdown of fat that can be used for energy. This metabolic shift has consequences on almost every system in the body. I know you don’t want me to detail each one and I’m not going to, but some systems have an important influence on how you will feel while eating the Ketogenic Mediterranean Diet. Let’s talk about those.
Energy Metabolism
The primary aspect of a ketogenic diet is that it forces your body to switch from using carbohydrates as its primary source of fuel to using fats instead. This is a two-stage adaptation process and can be a bit of a shock to the system.
First, as you deprive your body of carbohydrates, it will mobilize and disassemble the glycogen stores in your liver to provide glucose to cells throughout the body. The glycogen in your muscles will also get broken down, but it cannot leave the muscles. Once your glycogen stores are depleted, your body will believe itself to be starving and start to break down lean muscle mass so that it can continue to produce glucose. This is why it is recommended that you consume slightly more protein when embarking on a ketogenic diet pattern. Adequate sodium is important for lean mass retention, as well. I’ll explain why when discussing electrolyte balance (page 27).
The body cannot break down enough of its lean mass into glucose to cover all of its energy needs, so fatty acid oxidation will increase to make up the deficit. This process of glycogen depletion and fatty acid oxidation initiation will typically take two to three days. You may feel hungry, spaced out, or a bit cranky during this time. Thankfully, this period is brief.
Ketones are a byproduct of fat metabolism. There are certain parts of the body that require glucose. When there is not enough glucose available, the liver can turn protein into glucose to meet these needs. However, the liver itself requires energy in order to make glucose from protein. The liver can break down fat for energy but there are parts of the fat molecule that do not get used. These unused portions are transformed into ketones, which can be used for energy by most of the body’s cells.
The second stage of energy metabolism shift is colloquially referred to as fat adaptation, and it usually takes one to three weeks. During this time, the mitochondria in most of the cells of your body are adapting to use fat for energy more efficiently. If you have stayed in uninterrupted ketosis for three weeks, you will likely notice that you no longer get hungry in the same way that you did previously. You will still be hungry, but it will not be as drastic of a transition from high-energy satiety to low-energy hunger. In short, there will be no more carb crashes and no more episodes of feeling “hangry.” This is because, as we talked about in the last section, your body has hundreds of thousands of calories stored as fat at any given time. If you are fat adapted, these stores are much easier to access than a constant stream of glucose that needs to be replenished every few hours.
Weight Loss
As your body transitions from carbohydrate reliance to fatty acid metabolism, you will lose weight. Initially some of this weight will be water weight, because carbohydrates promote water retention and ketosis does the opposite. Beyond that water loss, you will lose some of your fat stores before reaching a stable equilibrium. If weight loss is one of your goals, you will need to eat fewer calories than you burn, just as with a traditional weight-loss plan. However, individuals typically find that adhering to a caloric restriction is easier when following a ketogenic diet pattern because fat leads to greater and longer-lasting feelings of fullness.
There are those who believe that being in ketosis will actually lead to a greater metabolic rate: you will actually burn more calories at rest than when you are eating a carbohydrate-based diet. There may be some truth to the idea that being in ketosis leads to greater weight loss because you are burning more calories, but a more likely explanation is that it is easier to lose weight when following the ketogenic diet because it is easier to adhere to a caloric restriction when eating foods higher in delicious fat. My personal experience with weight loss while eating a ketogenic diet reinforced this theory: When following a caloric restriction plan for the first few months, I was eating about a thousand calories less than the amount needed to maintain weight and I lost roughly two pounds per week during that period. It was delicious and effortless.
In addition to losing weight overall, you can rest assured that the weight you will be losing on a well-formulated ketogenic diet will be primarily fat and not lean mass. There are also indications that, to a greater extent than on a calorically restricted low-fat diet, the fat mass lost during ketosis comes from the abdominal trunk area. Excessive fat stores around the abdomen have been repeatedly associated with the greatest mortality and morbidity risks. Abdominal fat loss is a particularly interesting bit of ketogenic magic because it is the traditional belief that there is no way to target fat loss in a particular region of the body.
Blood Glucose and Energy Level Regulation
Individual reports and well-controlled research show that a ketogenic diet allows for much better blood glucose regulation than does the traditional high-carbohydrate diet pattern. From a physiological perspective, this makes perfect sense. Let’s go through it: when you eat carbohydrates they are broken down into glucose, in some cases very quickly, and enter your bloodstream. Your body deals with this glucose in one of four ways:
1. Burn it—Glucose can be burned, or metabolized, to be used for immediate energy. Obviously, the amount that your body will burn for immediate energy depends on your energy needs at the time.
2. Short-term storage—Glucose can be converted to glycogen and stored in the liver and in the muscles. As mentioned before, these are limited storage solutions, as the muscles collectively can hold about 400 grams of glycogen and the liver taps out at about 100 grams.
3. Long-term storage—When your immediate needs are met and your liver and muscle glycogen stores are full, your body will convert carbohydrates into a type of fat tissue called adipose for indefinite storage. Adipose tissue is what we typically think of as “body fat.” If there is an upper limit on the production of adipose tissue, it appears to be so high as to be meaningless.
4. Get rid of it—Colloquially referred to as “peeing it out” by my biochemistry professor in college, this is the body’s last option for dealing with the excessive glucose loads often thrust upon it by a carbohydrate-heavy diet. Typically, very little glucose leaves the body as waste because the body really likes to store energy, if it can. For most of human history, our food supply was not all that stable and it was not uncommon to rely on stored energy. However, in people that are not producing insulin or have insulin resistance, the body will produce more urine and shed more glucose in order to prevent blood glucose levels from getting dangerously high.
When consuming the SAD, your body is likely making frequent decisions about what to do with more carbohydrates than it can immediately use. The net result of this is often the production of new fat molecules from carbohydrates, called de novo lipogenesis (DNL), and fat storage. The problem is that all four of the above options for handling excess sugars can take several hours. In the time that it takes for these complex and multifaceted chemical processes to take place, you may experience a rise in blood sugar, which can induce negative results.
One to two hours after you eat, your body will have mostly broken down any carbohydrate in your foods and the resulting sugars will have entered your bloodstream. If you ate a lot of carbohydrates, a lot of glucose will enter your bloodstream and need to be dealt with. Some bodies deal with these glycemic loads more efficiently than others, but everyone on a SAD diet experiences at least a short period of time during which blood glucose levels rise before lowering again. Sometimes referred to as the “carb roller-coaster,” you may feel highly energetic after a carbohydrate-heavy meal and then very sluggish as your body manages to lower your blood glucose level again.
By contrast, when eating a very-low-carbohydrate ketogenic diet, your body uses the small amount of carbohydrates for brain and RBC fuel, and then makes the rest from protein or the glycerol backbone of triglycerides. This shift from a reactionary regulation of blood glucose levels to a proactive regulation is important. It allows for the body to keep blood glucose levels more even throughout the day, rely less on large loads of insulin, and keeps energy levels more consistent.
Electrolyte Regulation
Individuals initiating a ketogenic diet often notice that they need to urinate more frequently. Carbohydrates promote water retention, and so carbohydrate restriction and the subsequent breakdown of glycogen, which is anywhere from two-thirds to three-fourths water, results in the production of more urine and the loss of the electrolytes sodium, potassium, and magnesium. Additionally, insulin levels play a role in controlling how much sodium is retained. Lower insulin levels lead to a greater excretion of sodium by the kidneys.
Here is where the connection between sodium and lean muscle mass preservation comes in. Your body uses two types of cations, which are positively charged ions, to regulate the pressure and fluid levels between the fluid inside your cells (intracellular fluid) and the fluid outside of cells (extracellular fluid). These two cations are sodium and potassium. Sodium is the dominant cation in the extracellular fluid, and potassium is the dominant cation in the intracellular fluid. In order for your blood pressure to stay high enough and for your muscles to work properly, the balance of sodium and potassium has to be constant.
When your kidneys begin to excrete more sodium due to the physiological changes of ketosis, this balance can be thrown off. In an attempt to preserve this balance, the body will begin to excrete potassium, as well. The problem is that in order to do this, it needs to break down lean tissue to free the potassium. Therefore, if you do not properly replenish sodium while in ketosis, you run the risk of muscle loss driven by the body’s need for electrolyte balance.
Sodium, potassium, and magnesium are critically important to a whole host of functions within the body and their concentrations within the body are equally important. Too much or too little can be problematic, and mild deficiency of one or all three can cause some of the negative side effects associated with the initiation phase of ketosis. Often referred to as the “keto flu,” these side effects can involve low energy, headaches, muscle cramps, rapid heartbeat, constipation, and diarrhea. All of these symptoms can be explained by an electrolyte imbalance. In fact, the keto flu can be avoided altogether with electrolyte supplementation and replenishment. In The Art and Science of Low Carbohydrate Living, the authors recommend consuming five grams of sodium per day and taking a slow-release magnesium supplement.
Potassium should not be an issue for you while eating the Ketogenic Mediterranean Diet because you should be able to get adequate potassium from the copious amount of delicious vegetables you’ll consume.
Blood Lipid Regulation
Blood lipids include triglyceride and cholesterol levels. Triglycerides are a type of fat that your body uses for long-term storage. They are called triglycerides because they have a glycerol backbone with three fatty acids attached, causing them to look like an uppercase E. High triglyceride levels in the blood after an overnight fast are strongly associated with increased cardiovascular disease risk. The main factor in the elevation of fasting serum triglycerides is carbohydrate consumption. Carbohydrate restriction and ketosis have been shown to lower triglyceride blood levels very effectively. If you think about it, this makes perfect sense; when your body is relying on fat for fuel, there will be less available to hang out in your bloodstream.
Traditionally we think of cholesterol in three ways: total cholesterol, low-density lipoprotein cholesterol (LDL-C), and high-density lipoprotein cholesterol (HDL-C).
TOTAL CHOLESTEROL. This is the combined HDL-C and LDL-C circulating in your blood at any given time. Unfortunately, this number is not very useful for risk prediction. Generally speaking, clinicians will tell you that you should aim for your total cholesterol number to be equal to or less than two hundred milligrams of cholesterol per deciliter of blood. However, without more information, this number really doesn’t tell us anything about cardiovascular risk.
LDL-C. Both LDL-C and HDL-C are actually fats and proteins combined—that’s why they are called lipoproteins. Anyway, LDL-C is thought of as the “bad” type of cholesterol that you want to minimize and is associated with a greater risk of cardiovascular disease. It is thought that the reason higher LDL-C blood levels are associated with higher cardiovascular risk is that LDL-C can build up on arterial walls and restrict blood flow over time.
HDL-C. High-density lipoprotein is thought to be the “good” variety of cholesterol and higher numbers are associated with lower risk. We believe HDL-C to be “good” because it travels through the bloodstream collecting cholesterol and transports it out of the bloodstream.
Importantly, the ratio of total cholesterol to HDL-C seems to be a better predictor of risk than any of these numbers alone. The ideal ratio is said to be less than 3.5 to 1.
Emerging science in the area of cholesterol and heart disease tells us that this picture is much more nuanced than we currently understand. As with most advances in knowledge, research findings take a long time to make it into common practice but our understanding of the complex role of fats in our diets is getting better all the time. One thing that research has consistently shown is that the ketogenic diet reduces serum triglyceride levels, decreases LDL-C, and increases HDL-C.
APO A AND APO B. I mentioned above that HDL-C and LDL-C are actually combinations of fat and proteins. Apolipoprotein A (apo A) is a constituent found in HDL-C, and apolipoprotein B (apo B) is found in LDL-C. Researchers have been finding that the ratio of apo B to apo A is a better predictor of cardiovascular risk than that of HDL-C to total cholesterol. However, reference ranges have not been standardized and testing is still not widely used. Ask your physician about this test and ratio if you are curious. This will both spread awareness of its use, if your physician is not yet aware, and increase your knowledge of your particular cardiovascular risk.
LDL-P. While LDL-C measures the concentration of cholesterol in the particles of LDL, it does nothing to indicate the actual number of LDL particles. That’s what the P in LDL-P is: particles. This is a measurement of how many LDL particles are in your blood. Interestingly, this looks to be an even more accurate predictor of cardiovascular risk than any of the previously mentioned ratios. Early evidence indicates that the ketogenic diet improves LDL-P levels, as well. However, research still needs to be done before any type of clinical usefulness can arise from this measure.