Maybe you have noticed that there has been a movement from the old adage of a low-fat diet to a low carb diet. Most people who come to me have tried some version of a “keto” diet. I am concerned because when I take the dietary history from many people, there is a high prevalence of foods that are associated with increased risk of cardiovascular disease. This means that while their weight may be coming down, their risk of cardiovascular disease may be going up. Yes, you heard me right, you can lose weight and potentially not have your risk of the most common cause of death go down. That is called an association, not a causal relationship. Eating for weight control and eating for cardiovascular disease prevention are not necessarily the same thing. We want to find that sweet spot (pun intended) that both controls weight and has been shown to reduce cardiovascular disease risk. So, what is it? What is the best nutritional pattern to follow once you reach your goal weight and have completed the medical protocol portion of your weight loss phase of your program? Well, I wish there were a simple answer, and maybe there is, but do not skip to the bottom of this blog!
As you know, many things in the world follow a pendulum swing. What was old, is new again, and vice versa. Your grandparents probably ate whole eggs and bacon for breakfast with butter. Sound like a keto diet? Then, in the 1970s, the American Heart Association started recommending a low fat diet. What happened after that was the replacement of fat in foods with fructose and other substances that increased their shelf life and their palatability and created what is known as highly processed foods that compose such a large portion of the typical American diet today. This was shortly followed by an uptick in the rates of obesity, Type 2 Diabetes Mellitus, and cardiovascular disease that continues today. Cardiovascular disease remains the cause of death of one-third of people, and is likely only controlled by the advents of pharmacologic and procedural interventions which increase the population’s dependence on the healthcare system. What happened next? Well, the pendulum has swung the other way, and there is a (somewhat) underground, anti-establishment movement of a keto diet or somewhere in between the spectrum of a low fat and keto diet. If the keto diet works to control blood sugar and weight, what is the problem and why isn't your cardiologist recommending it? Well, the problem is what people are eating instead of the carbohydrates. Whereas a low fat diet may have caused a rapid increase in obesity, a low carbohydrate diet with increased saturated fats may cause an increase in cardiovascular disease even if it causes a shorter term decrease in weight and Type 2 Diabetes Mellitus.
Oh no, I think I have made this more confusing, not less. Let’s look at each macronutrient separately, because, by now, you must be wondering, “Okay, Doc, what am I supposed to EAT?!”
So, how do you eat carbohydrates without them being “bad” for you? Well, just like fats and proteins, not all carbohydrates have the same effect on your health. This study shows that fructose increases the markers linked to fatty liver, atherosclerosis, and Type 2 Diabetes, but glucose does not. Why is that? Well, fructose is metabolized only by the liver, and increases signals that increase triglycerides and adipose tissue creation, whereas glucose is used as energy by all of the cells in the body, such as the brain, kidneys, and skeletal muscle.
So, you have heard that carbohydrates are “bad?” Well, the other side of the story is that this paper published in the Lancet (a very well respected journal) in 2018 showed that both high and low carbohydrate diets were associated with increased mortality (risk of death). It further showed that the lowest risk of death was, you guessed it, right in the middle, at 50-55% energy from carbohydrates. Does this mean you need to eat that many carbohydrates? No, it does not, because then your weight may go up and cause different problems. This paper acknowledges what we are going to talk about next, the problem with low carbohydrate diets is probably not removing the carbohydrates, it is what you might be eating instead of them. This leads us into the topic of different types of fats.
Fat - Villain or Bad Wrap?
A “keto” diet is a low carbohydrate, high fat diet. I am concerned because I frequently encounter the situation where a person is meeting their energy needs when they have reduced carbohydrates by increasing saturated fats and processed meats, and are still exceeding total caloric needs on a daily basis. This position statement by the American Heart Association makes three important conclusions, by my interpretation:
Saturated fats should be <6% of total energy intake (reduced from prior recommendation of <10%.
Total dietary intake of fat does not need to be reduced (different from the low-fat recommendation that was villified by the “keto” camp).
N-6 polyunsaturated fats are better for you than monounsaturated fats, but either one is better than saturated fats.
What is the breakthrough from this position statement? Well, they address the elephant in the room of the studies used to argue for a low carb diet that show that a diet low in saturated fat does not lower cardiovascular disease by arguing that it is because the saturated fat calories were replaced by, you guessed it, the fructose we addressed in the carbohydrate section above. They use as evidence the pivotal study that showed prevention of cardiovascular disease by supplementing a Mediterranean diet with olive oil or nuts compared to a low fat diet.
So, when thinking about “learning how to eat”, remember that we eat food, not macros or calories, and that not all carbs or fats affect the body equally, and no, glycemic index is not the answer, either.
My take away messages are:
A low carbohydrate diet can be an effective tool to control weight in the short, medium, or long-term time frame, but the substitution for those calories should be well-formulated so as to avoid an inadvertent increase in a competing risk.
A diet in which as much as 50-55% of energy is derived from carbohydrates has been associated with the lowest risk of mortality. A low carbohydrate diet is not the only “healthy” diet.
A diet that controls weight by increasing saturated fats may lower body weight but may increase cardiovascular disease.
I hope that I have made a case for the fact that “low carb” is not the whole story, by any means, of how to eat. I know I may have made more questions than I have answered, but sometimes, you have to tear some things down before you can build them back up!
For now, the “Cliff’s notes” version (who remembers those yellow black stripes?) if you are wondering what to eat for dinner tonight is to eat vegetables soaked in olive oil with fish and nuts on top. If you do not have carbohydrate intolerance, have some whole grains. If you have excess weight affecting your health, limit the total calories. Incorporating this into a weight management program takes individualization and a comprehensive approach.
Take Back Your Health,
Valerie Sutherland, MD