All about fats, what every distant runner should know.

Why are Fats Important? 

Fats (fatty acids) are the primary energy source used at rest and during low to moderate exercise. Fats have the highest concentration of energy of all the macronutrients (9 kcal/g vs 4 kcal/g in carbs and proteins). In addition to their importance for supporting our energy needs- both at rest and during exercise, dietary fat intake is needed to obtain essential fatty acids, and for the absorption of fat soluble vitamins. Fats also provide insulation and protection to organs, provide structure to cells, and are required for the synthesis of hormones. In summary, some important roles of fat include: 

• Significant energy source- at rest and during low to moderate exercise

• Dietary fats are needed to provide essential fatty acids (discussed below)

• Required for the absorption and utilization of fat soluble vitamins

• Provide insulation- protects organs

• Provide structure to cells

• Needed for hormone synthesis

Fat as Fuel- Importance of Our Endogenous Fat

During endurance activities, the aerobic energy system is primarily being utilized, and fatty acids are the primary energy source being oxidized at low to moderate intensities. As the duration of exercise continues, there is an increased utilization of fatty acids as fuel. 

The circulating and stored fat in your body does not all come from dietary fats, rather, they are the result of carbohydrate, protein and fat metabolism. In other words, breakdown of all 3 macronutrients can result in fatty acid synthesis for the body to use for fuel, storage, and to synthesize other lipid-containing molecules. 

During high intensity exercise, the body’s primary fuel source is carbohydrates since that is the only substrate that can be utilized for energy in anaerobic conditions. However, as carbohydrate stores (liver and muscle glycogen) get used up within several hours of exercise, the body shifts towards utilizing a higher proportion of fats in relation to carbohydrates as fuel. During this shift, the athlete is also forced to lower their intensity to support the increased demand for oxygen and the slower rate of energy provided by other sources (i.e. fatty acids, amino acids) 

When exercise intensity is moderate (65% Vo2max), intramuscular fatty acids are the primary fuel source utilized. During low intensity exercise (<50% Vo2max), plasma fatty acids (supplied from adipose tissue) are primarily utilized, and their contribution increases as duration increases.   

As an athlete becomes more trained, they increase their ability to oxidize and utilize a higher proportion of fat (in relation to carbohydrate) at the same absolute intensity. This is a favorable situation since the athlete will spare glycogen, which can then get utilized when the demand for intensity increases. 

Dietary Fats

How much fat do I need each day? 

This is not a straightforward answer since it depends on the total energy needs as well as carbohydrate and protein requirements.  Unlike protein and carbohydrate recommendations for athletes (which are ?? on a gram per kilogram of body weight basis), dietary fat requirements are expressed as a percentage of total energy intake.  General guidelines are as follows:

• Aim for a range of 20-30% of total calories coming from fats; chronic consumption of <20% may negatively impact the athletes health and performance (see below)*.   

• Include the AIs for EFAs here too. 

*Complications of Very Low Fat Diets

Athletes consuming very low fat diets (<10%) often are not able to meet their energy needs. A very low-fat diet may also have the following consequences: 

• Impaired endurance performance (due to inadequate intramuscular triglyceride) 

• Inability to meet essential fatty acid requirements 

• Limited intake and absorption of  fat soluble vitamins

• Menstrual dysfunction

When is the best time to consume fats? 

It’s probably easier to answer this question by identifying when it is NOT a good time to eat fats and that is within 2 hours before, during and immediately after exercise. 

Fat slows gastric emptying, which is one of the reasons it contributes to satiation. While this is a good thing to curb hunger during a busy day, it is not ideal before or during running since undigested food can cause an upset stomach. Additionally, the slowed digestion will also slow the rate of nutrient absorption, including the glucose needed for immediate fuel. Fats are not an effective fuel for rapid energy as carbohydrates are. Therefore, it’s best to shy away from foods high in fat in your pre-run meal and choose carbohydrate fuel sources during your run, over high fat foods. 

For the same reason that high fat foods should generally be avoided before and during exercise, it is wise to make sure carbohydrates and proteins are at the forefront of your post run snack or immediate post run meal. If the meal is rich in high fat foods, this not only slows the uptake of amino acids and glucose needed for replenishment, the fat may be taking precedence over the total carbohydrate and/ or protein content of the meal or snack. To be clear, certainly include healthy fat sources in your post run meal to meet overall daily energy and nutrient needs, but prioritize meeting your protein and carbohydrate requirements.

What are the best types of fats to consume? 

Fats can be classified as saturated, unsaturated and “trans”. The healthier types of fats are in the unsaturated category. In general, the foods offering the highest proportions of unsaturated fats are plant-based fats- with the exemption of fatty fish also offering a high amount of unsaturated fats, while coconut and palm oils have a less favorable fat profile. 

Considering plant-based foods and fatty fish provide healthy fats, including the essential fatty acids omega-3 and omega-6, it’s wise to get the majority of our fat through these foods, while limiting fats from animal-based products, coconut and palm oils, and highly processed foods- which are generally higher in trans fats. 

Meeting daily requirements for omega-6 fatty acids is fairly easy since LA is plentiful in a wide variety of foods. Omega-3 fatty acids are more difficult to obtain since they are limited to a select few foods. The omega-6 to omega-3 fatty acid ratio to aim for is 4:1; higher ratios, as seen in the typical American diet (estimated to be 15:1) have been shown to cause inflammation. 

ALA is an inactive form of omega-3 fatty acid, whereas EPA and DHA are active forms. The conversion of ALA to EPA and DHA is not very efficient; this is not a concern for individuals who consume fish regularly, but may pose concern for non-fish eaters. Even if ALA intake is high (only in plant foods, some listed above), individuals may still be falling short on meeting their EPA and DHA needs- due to the inefficient conversion. Does this mean you should supplement with EPA and DHA (fish oils)? See my answer to this question below. 

Are Fish Oil / Omega-3 Supplements Necessary? 

Taking fish oil supplements have not been shown to improve athletic performance, or have any improvement on inflammation, injury, or immune functions. It is best to get your essential fatty acids through your foods. However, if you are not able to obtain adequate omega-3 fatty acids in your diet, supplementation may be a good idea!

Some Good Options:

1. Consume fatty fish (e.g. ) several times per week, as part of nutritionally balanced meals. Some examples of fatty fish include: tuna, salmon, herring, sardines, and mackerel.

   • Consume the plant sources of ALA for their additional health benefits and to further boost your DHA and EPA bioavailability  

2. If you do not eat fish, the next best option is to consume food sources rich in ALA (ground flaxseed, walnuts, leafy greens, etc) since they have additional health benefits aside from offering the inactive form of omega-3 fatty acids. 

   • Supplementing with fish oil or microalgae oil providing both DHA and EPA to cover your bases may be beneficial since the conversion of these essential fatty acids from ALA may be inefficient

In regards to athletic performance, omega-3 fatty acid supplements- such as fish oil supplements, do not have any benefit on athletic performance. They have not been shown to decrease inflammation or muscle injury, nor do they have any benefits in boosting the immune system- as popularly claimed. The only benefit that omega-3 fatty acid supplements demonstrated in athletes were protective effects of exercise-induced bronchoconstriction in athletes with asthma.

Note that if you decide to take omega-3 fatty acid supplements, there is such a thing as too much of a good thing! High supplemental doses may interfere with the body's ability to counteract oxidative stress. High supplemental doses of 3g/day have been shown to damage the membranes of red blood cells, and increase biomarkers of postexercise oxidative stress. (reference)

Guidelines for omega-3 fatty acid intake: 

• Do not exceed 3 g/d EPA and DHA (from diet + supplements) 

• Do not exceed 2 g/d from supplements 

References

Mickleborough, Timothy D, Lindley, Martin R, Ionescu, Alina A, and Fly, Alyce D. "Protective Effect of Fish Oil Supplementation on Exercise-Induced Bronchoconstriction in Asthma." Chest 129.1 (2006): 39-49. Web.

Malaguti, Marco, Baldini, Marta, Angeloni, Cristina, Biagi, Pierluigi, and Hrelia, Silvana. "High-protein-PUFA Supplementation, Red Blood Cell Membranes, and Plasma Antioxidant Activity in Volleyball Athletes." International Journal of Sport Nutrition and Exercise Metabolism 18.3 (2008): 301-12. Web.

Dunford M & Doyle JA. Nutrition for Sport and Exercise 4th ed. Cengage. 2019.

Rebecca Wall, R Paul Ross, Gerald F Fitzgerald, Catherine Stanton, Fatty acids from fish: the anti-inflammatory potential of long-chain omega-3 fatty acids, Nutrition Reviews, Volume 68, Issue 5, 1 May 2010, Pages 280–289, https://doi.org/10.1111/j.1753-4887.2010.00287.x