There is a lot of conflicting information out there regarding fats and how they relate to performance nutrition. During the ‘80s and ‘90s there was a push towards low-fat diets, with many believing that fat was the ultimate bad guy when it came to nutrition. There were several things that factored into this thinking, but the two big things were that 1) reducing fat intake led to a decrease in cardiac related mortality and 2) because fat is more energy dense than carbohydrates, it is easier to achieve a caloric deficit by reducing fat intake. Now the push seems to be heading back in the other direction with keto diets, Whole30, and other such high fat diets. So which diet is more effective? What are the risks and benefits associated with each? Those are the questions I will answer in this article.

                First things first, before deciding whether to go low fat or low carb, it is important to understand what fat is and its application in performance nutrition. Fat is a macronutrient that is comprised of triglycerides, and there are several types of fats: saturated fats, unsaturated fats, and trans-fat. The structure of the fat molecule determines its nutritional value. Without getting too far into the weeds with chemistry, the type of fat is determined by the presence and location of double bonds between carbon atoms within the chemical structure of the fat molecule, with saturated fat having no double bonds and unsaturated fat having at least one double bond. Trans fat is often portrayed as the “bad guy” right next to simple sugars, and in this case it is true. Trans fat is fat in commercial products that have been artificially hydrogenated (converted from unsaturated fat to saturated fat) in order to improve the taste and shelf life of many commercially produced products. However, trans fat has been linked to elevated risks of heart disease and inflammation within the body. Trans fat has essentially no nutritional value and should be kept out of the diet as much as possible. Regardless of the type of fat, a gram of fat contains nine calories and is used as the body’s slow burning fuel source. Studies indicate that when the body is in a resting fasted state, it is primarily using fat as it’s fuel source. Now let’s talk about how fat plays into performance nutrition.

                As we discussed in my article on carbohydrates, carbs are the body’s primary source of energy. However, there is only a certain amount of glycogen stored in the body, so the body burns different energy sources based on the level of exertion. In lower levels of exertion, the body relies more on fat as it’s energy source. This is why many endurance athletes are on high fat diets. As exertion increases and heart rates increase the body switches from burning primarily fat to burning primarily carbohydrates, which is known as the “crossover”. The crossover is not well understood yet and varies in each person. Serving as an alternate has an added benefit, which is nitrogen sparing. In my article about protein, I briefly talked about how protein can be used as an energy source if other sources of energy were not available. Fat and carbohydrates prevent this when they are present in adequate amounts, which is known as nitrogen or protein sparing. This is another reason why athletes should consume adequate amounts of fat in their diet, so the protein can go towards its intended purpose of building and repairing tissues in the body.

                Along with serving as an energy source, certain types of fats have beneficial pharmacological roles in the body. Most notably among these are Omega 3 and Omega 6 fatty acids, which are known as essential fatty acids because the body is not capable of producing them. These are commonly found in fish and animal products. However, just because they are labeled as “essential” does not mean you should go crazy with supplements. The recommended ratio between Omega 6 and Omega 3 fatty acids is 5:10. However, most Americans consume a ratio of 50:1 Omega 6 to Omega 3. So, an Omega 3 supplement is highly recommended. When consumed in appropriate amounts, these essential amino have been shown to reduce arrythmias in the heart, improve muscular recovery, and reduce inflammation throughout the body. A good source of supplementation for Omega 3s would be either krill oil or fish oil.

                Now that we’ve covered the basics of fat let’s break down the low carb/high fat versus high carb/low fat diets and which would be more beneficial, and which diet I would recommend. Let’s start with the high carb/low fat diet. The number one reason people tend to go with the low fat diet is the simple fact that they are counting calories more than counting macros, and it is easier to stay under a caloric goal if you avoid fats because they are a more energy dense nutrient source. However, studies have shown that people who consume low fat diets are deficient in the fat-soluble vitamins (A, D, E, K), while also having a reduction in sex hormone (estrogen/testosterone) production. This is detrimental to athletic performance for many reasons. The fat-soluble vitamins are responsible for functions in the body such as calcium absorption, whereas the sex hormones have a huge role in muscle synthesis and energy levels. Finally, the more fat there is in the diet, the more the body becomes adapted to using fat as an energy source. This means that in a low-fat diet, the body is less willing to use stored fat as an energy source, which makes burning body fat much more difficult. Now let’s look at low carb diets. Low carb diets have lower insulin levels in the body which facilitates lipolysis (the breakdown of fat in the body), and have a superior nitrogen sparing effect compared to low fat diets. However, low carb diets have also been shown to slow down glycogen synthesis after exercise which can lead to longer recovery times. In addition to this, low carb diets are generally low in dietary fiber, which I covered in my article about carbohydrates.

                So which diet do I recommend? The short answer is neither. I am a big believer in the age old saying “everything in moderation”. As we’ve discussed, both carbohydrates and fats play crucial roles in performance nutrition and should be consumed in appropriate amounts. I typically recommend that fats comprise between twenty-five to forty percent of an athlete’s daily caloric intake depending on what their goal is. Remember, no macronutrient is “bad” if it is within your daily macronutrient goal and it is coming from a good source. Speaking of good sources of macros, I’m going to finish this article with a table with the sources of fats and what to avoid. As always, if you have any questions, let me know!

Best sources of fats

Decent sources of fat




Heavily processed meat

Egg yolks

Bacon fat

Processed cheeses


Hard cheeses

Anything containing trans fat


Dark chocolate

Heavily processed oils

Grass fed butter


Heavily fried foods

Fish oil



Natural cold pressed oils





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