The Science of Your Diet


Every diet is unique—understanding how they work with your body is key to choosing yours

I really disdain most articles written about diet. You see them on the front pages of the various magazines at the grocery store check out lines. They seem to be much more frequently advertised on every social media feed, as well. These articles are generally espousing the virtues of the latest fad diet generally centered around fat loss. This is not that kind of article.

I have been an been an orthopaedic surgeon for more than 20 years, and as such, I have operated on thousands of patients. I have seen first-hand that the nutritional status of the patient makes a big difference in their recovery. As a result, I have spent years developing an understanding of the science of nutrition.  I implore my patients to review the recommendations on my website on how to nutritionally prepare for and recover from surgery.

That’s what this article is about, a deep dive into the science behind your diet, with the hope being that you will be able to read and consider the best diet for you based on not only your desires and goals, but also your metabolic health.

Fat loss is the most common driver for starting a new diet so we will use this as a springboard. This desire is highlighted by the exponential increase in the use of semaglutide as a means to reduce weight. If you recall from my last article, semaglutide is a peptide. Peptides can be used to increase the function of a cell or organ to secrete a desired substance such as a hormone. Semaglutide, in particular, works by mimicking the GLP 1 receptor which, in the gut, makes you feel full and, in the brain, makes you feel satiated. I frequently get asked about dietary supplements and medications for this purpose, but until you get your nutritional and exercise house in order, it is a moot point but one we can explore later.

All diets involve some kind of restriction. The most common are caloric restriction (simply reducing the total calories consumed), time restricted eating (intermittent fasting), or restriction of some food type and thus increasing another (carnivore, vegan, vegetarian, keto, low carb, etc). One of my favorite quotes is from Thomas Sowell as it applicable to most situations in life: “There are no solutions, just tradeoffs.” This applies to our diets.

The Basics of Restricting Calories

Caloric restriction is based on the concept of CICO (calories in vs calories out). At its very basic level, this equation is true, but let’s try to make this more actionable. I have heard people say that all calories are not the same. This is as silly as saying that all seconds—whether we’re talking time or trips to the buffet—are not the same. Obviously, all seconds are the same, it just matters what you do with them. A calorie is simply a unit of energy and more specifically heat. It is the unit of energy needed to raise the temperature of 1 gram of water by 1 degree Celsius. Where you derive these calories does matter.

This leads us to the thermic effect of various food types. The thermic effect of food takes into account how many calories are required to metabolize the substance. Fat has a thermic effect of about 3 to 5 percent, carbohydrates around 8 to 10 percent and protein is a whopping 20 to 30 percent. That means that if you consume 100 calories of fat that you will net about 95 calories while if you consume 100 calories of protein you will net 70 calories. This might be one of the reasons that we get the “meat sweats” after a good ribeye.

Caloric restriction seems to have additional health benefits besides weight reduction. Mice that have been calorically restricted (compared to those allowed to eat ad libitum) lived longer and had a decrease in the development of cancer. This has not been replicated in humans to my knowledge but is interesting data, nonetheless.

Caloric restriction can be easier if we understand satiety. We tend to eat and feel satiated based on food volume and protein content. Two equal volumes of food can have vastly different caloric content. Choosing foods with lower caloric density will allow you to eat less and feel satiated. In general, the higher the water and fiber content and lower the fat content of the food will result in lower caloric density. Low caloric density foods include fruit, vegetables and meat. High caloric density foods tend to be dehydrated like chips or high fat content like candy bars.

The Fasting Facts

Time restricted eating or intermittent fasting has become popular and to some degree can work via the same mechanism as caloric restriction. You are simply not eating as many calories in your feeding window. There however appear to be some differences. When fasting, the body will start running low on available glucose and start mobilizing fat and some glycogen stores and go into a state of ketosis. Ketosis is the formation of ketones from the metabolism of fats as a fuel source. This shift to using fat as the fuel source and the reduction in blood glucose results in a reduction of insulin. Hyperinsuliemia, insulin resistance, and metabolic syndrome are all related problems and affect 36 percent of Americans. Reducing circulating insulin levels is a critical component to the prevention of these problems and the development of diabetes.

In addition, the fasting state induces the body to shift from being in an anabolic state (growth) to more of a catabolic state (decrease in cell division and growth). Enzymes like mTOR (mechanistic target of rapamycin) decrease in activity which causes the cells to replicate less and focus more on cleaning up old cellular debris. This clean-up process, or cellular autophagy, is associated with a reduced risk of cancer.

Restriction Revelation

Restriction of various food types in lieu of others is a very vast topic and is wrapped up not only in nutritional preference but also philosophical ideals. The carnivore versus vegetarian debate can become very heated. Let’s look at some basic principles to help guide a reasonable diet.

As we discussed in our section on restricting calories, there are three main food types: fat, carbohydrate, and protein. We need all of them to survive. Fat or lipids includes triglycerides and cholesterol and are critical as they form the outer structure of the cells and hormones. Carbohydrates are a primary fuel source of which glucose is the most common. Proteins form the building blocks for our bodies and enzymes for metabolism.

In general, about 50 percent of a carbohydrate/glucose load is burned and expelled as CO2 and H2O as we breathe, 5 to 10 percent is stored as glycogen and the remaining 40 percent is stored as fat. The point is that we pretty much have an unlimited ability to store excess energy as fat, but very little ability to store protein. There is a small pool of available amino acids, but most of our protein is used for structural building. While we can and do use protein as a fuel source, it is not very efficient and is better used to build and run the body. Personally, this is why I like a high protein diet, which is usually around 1 gram per pound per day.

The ketogenic diet or very low carb diet has benefits as well. As stated earlier, it can markedly reduce insulin resistance and is therefore a good diet for diabetics. The ketogenic diet was originally designed to help patients with seizure disorders. It can reduce the incidence of seizures by 60 percent, in most studies. The types of fats consumed on a ketogenic diet are important. Saturated fats (no double bonds in the carbon chain) in general increase your LDL (low density lipoprotein) level. Your LDL level and more specifically apoprotein B level (the carrier of LDL) is one of the strongest predictors of atherosclerotic disease. Atherosclerosis is the hardening of the arteries and causes heart disease which is by far the most common killer in the world. Monounsaturated or polyunsaturated fats are a better choice.

No matter the diet, one of the most important aspects of your diet is the amount of soluble fiber. Soluble fiber is a prebiotic used by the bacteria in your gut which they ferment into short chain fatty acids. One of the fatty acids, propionic acid, inhibits an enzyme in your liver that makes cholesterol. Many of the statin drugs act by inhibiting this same enzyme. So just through diet, you can lower your cholesterol. Also, high fiber diets have been shown to reduce inflammatory markers such as CRP and IL-6. Finally, it has been demonstrated that for about every 10 gram increase of fiber in your diet, you can reduce your risk of heart disease and stroke by 10 percent with high fiber diets boasting a 24 percent decrease. It is recommended to get about 15 grams of fiber for every 1,000 calories. This is best done through fruits and vegetables. A smoothie in the morning with fruit and vegetables and protein powder of choice is a simple way to do this.

Finding What’s Right for You

Although there is no one perfect diet for everyone, high protein and soluble fiber with minimal saturated fat seems to be optimal. Most importantly, you have to choose a diet to which you can adhere. Consistency is the key for results in dieting and exercise. Make your diet and exercise a habit. One of my other favorite quotes is from James Clear in Atomic Habits. “Habits are the compound interest of self-improvement. The same way that money multiplies through compound interest, the effects of habits multiply as you repeat them. They seem to make very little difference on any given day and yet the impact they deliver over months and years can be enormous.”

Clear had it right.  Making healthy choices habitual is a must for leading a healthy life.  If you are unsure where to start, let this article get you moving, and then speak with your doctor and ask questions. Through conversation with someone who understands more about how your body reacts to a variety of factors, you will find your optimal diet.  However, don’t forget that diet is only half of the equation.  See you at the gym! 

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