How Much Fat Do You Really Need?

Fat is demonized.

We see it in plenty of products that are labeled as low-fat or fat free. 

But fat serves vital functions in your body, such as:

  • Being a readily available form of stored energy
  • Protecting vital organs
  • Insulation
  • Absorption of vitamins
  • Cell membrane structures
  • And plenty others.

However, fat can add up pretty quickly, so it’s important to watch how much fat you eat. That’s because one gram of fat = 9 calories, so its caloric content is 2.25x that of carbohydrates or protein. 

Fat is a misunderstood nutrient by many. 

That’s why I’ve decided to get a better understanding of fat. I recently completed the ACE Fitness Nutrition Specialist course. In one of the manuals, Sports Nutrition for Health Professionals (2nd. Ed.), the authors discuss fat. The end of the chapter that discusses fat in detail has two case studies looking at fat needs for a:

  • Middle-aged woman hiking the Grand Canyon
  • Triathlete looking to improve his performance.

Becoming a Fitness Nutrition Specialist will help you develop expertise in all areas of nutrition education and promotion that are within the scope of practice for health and fitness professionals.

Let’s learn about two types of people and what their fat needs look like. 

Case 1: Susan, The Middle-Aged Overweight Hiker

Susan is a 55-year-old overweight teacher who has struggled with her weight since childhood. After her best friend suffered a debilitating heart attack, she decided to change her lifestyle and achieve a healthier weight. As part of her fitness program, she is training to hike the Grand Canyon with her 17-year-old daughter and a guide. She is 5’2” and 180 pounds (BMI 32.9 kg/m2). According to the National Institute of Health’s Body Weight Planner, Susan needs about 2,000 calories per day to maintain her weight. 

What is the acceptable macronutrient distribution range (AMDR) for fat intake? 

The Institute of Medicine estimates the AMDR (i.e., how much of a particular macronutrient you should eat) for fat at 20-35 percent. “These ranges allow for sufficient intakes of essential nutrients,” says the IOM, “while keeping the intake of saturated fat at moderate levels.“

What range of calories per day should Susan get from fats to maintain her weight? 

With Susan eating 2,000 calories to maintain her weight, and given the AMDR, Susan should eat 400-700 calories of fat per day.


Susan tells you that she is confused as to whether fat in her diet matters or not. She says that the last she remembers, the recommendation was to eat a “low-fat” diet but then she heard that the Mediterranean diet, which is high in olive oil and fatty fish, is very healthy, and now she has read a lot of information that says “saturated fat is good.” She asks you to please clarify which fats are “good,” which are “bad,” and what she should be eating. 

Susan has every right to be confused here, and there’s so much to unpack that I could make a separate post. 

For now, I would tell Susan that she should target her AMDR of 20-35% of calories coming from fat using the numbers listed above. 

I would also tell her that she can consume saturated fat, but the recommendation is that less than 10% of fat intake should come from saturated fat. In other words, if her fat intake is on the lower end at 400 calories, a maximum of 40 calories of fat could come from saturated fat. That’s less than a tablespoon of coconut oil

The Mediterranean diet, in particular, features more calories coming from fat than the typical American diet, but is associated with a decreased risk for a number of conditions such as heart disease and cancer. 

Case 2: Scott, The Professional Triathlete

Scott is a 29-year-old professional triathlete. It is the off-season and his current training program is of relatively low intensity. He is 6’2” and 170 pounds (BMI 21.8 kg/m2). He needs about 3,200 calories per day to maintain his weight.

What is the AMDR for fat for athletes?

Athletes typically have differing protein and carbohydrate needs compared to the general population.

That’s not the case with fat consumption—athletes should eat roughly the same amount of fat as anyone else.

According to the text, “athletes are advised to consume fats within the AMDR of 20% to 35% of total calories.”

What range of calories from fat should Scott get each day? 

At 3,200 calories to maintain his weight, Scott should eat within 640-1,120 calories of fat per day.


How might Scott’s fat needs within this range change over the course of the year? 

As Scott’s training needs increase closer to competition, he’ll likely want to consider eating more carbs and less fat. He’s got plenty of wiggle room:

  • AMDR for fat: 20-35%
  • AMDR for carbs: 45-65%

However, Scott should consult with a registered dietitian to get specific advice on his calorie intake.

Scott has experimented with several dietary manipulations during the off-season in an effort to identify a regimen that will give him the competitive edge during the training and competition seasons. He has recently started a fat-loading diet with the following regimen:

Day 1Day 2Day 3Day 4Day 5Day 6Day 7
NutritionHigh-fat diet (70% of calories from fat, 15% carbohydrates, 15% protein)High carbohydrate (70% carbs, 15% fat, 15% protein)
ExerciseRun for 20 min at 70% VO2max + interval trainingRide 3-4 hoursRun 2 hoursRide 3-4 hoursSwim 1.5 hoursRest“Brick”
(45-min swim, 2-hour ride, 1.5-hour run)

Describe the rationale behind “fat loading.” Include a discussion of “fat adaptation.”  What are the pros and cons of the dietary plan (called “dietary periodization”) that Scott is following? What advice do you have for Scott as he experiments with his diet/training regimen? 

First, let’s address the dietary periodization Scott follows. 

Why Use Dietary Periodization?

‘”’Dietary periodization’ involves the manipulation of macronutrient intake in association with changes in physical training,” write the authors of Fat and Carbohydrate for Exercise. “Such interventions have a major effect on altering patterns of fuel utilization during exercise; however, they often fail to enhance performance capacity.” 

How Does Fat Loading Create Fat Adaptation? 

The idea behind fat loading in athletes is to increase fat consumption for using fat as an energy source. As a result, carbohydrate energy stores can be spared. Carbs only fuel about 3 hours of endurance activity, so the rationale behind fat loading is that it will take longer to deplete muscle glycogen so that an athlete can maintain long-distance activities for a greater amount of time.

The challenge is that fat loading doesn’t appear to work. 

Selected highlights from a review of available journal abstracts support the use of carbohydrates for energy over fat:

  • “It appears prudent to advise endurance athletes to consume a diet that is largely carbohydrate to optimize training and competitive performance and, more importantly, to promote optimal health.” Fat Loading: The Next Magic Bullet?
  • “When exercise intensity is increased, there is an increased need for carbohydrates. On the other hand, consumption of a fat-rich diet decreases the storage of glycogen in both muscle and liver. Therefore, training intensity may be compromised in individuals while consuming a fat-rich diet.” Long-term Fat Diet Adaptation Effects on Performance, Training Capacity, and Fat Utilization
  • When adaptation to a fat-rich diet was performed over longer periods, studies … demonstrate either no difference or an attenuated performance after consumption of a fat-rich compared with a carbohydrate-rich diet. When performance was measured at high intensity after a longer period of adaptation, it was at best maintained, but in most cases attenuated, compared with consuming a carbohydrate-rich diet.” Adaptation to a Fat-Rich Diet: Effects on Endurance Performance in Humans

With years of research slamming the use of fat for fuel, I would not recommend fat loading unless specifically prescribed by a registered dietician or physician. 

Train Yourself

What is the recommended AMDR for fat for you?

Using the National Institute of Health’s Body Weight Planner, estimate your daily caloric needs. Based on that estimate, what range of calories from fat should you get each day? 

The Body Weight Planner estimates my daily caloric needs to be 2,986 calories to maintain my current body weight of 175 pounds given my activity level. (I don’t buy into this all the way, though, since I can maintain my body weight at 2,500 calories).

Given this, my AMDR falls between 597 (20%) and 1,045 calories (35%).


Record your food intake for a 24-hour period using MyFitnessPal.

What is the percentage of calories from fat? How does this compare to the AMDR? 

Personally, I’ve set my own fat intake at 30%, which is within the AMDR. That’s 77 grams, or 693 calories from fat. 

How many grams of saturated fat did you eat? What percentage of total calories came from saturated fat? List several of the fatty foods that you ate. Using the USDA National Nutrient Database or MyFitnessPal, determine the amount of various types of fat in each of the foods. Rank saturated fat, polyunsaturated fat, and monounsaturated fat from “most eaten” to “least eaten.” 

On this particular day, I ate 15 grams of saturated fat. 

FoodFat TypeAmount (g)
EggsPolyunsaturated fat4
ButterPolyunsaturated fat2
Whole wheat breadPolyunsaturated fat1
EggsMonounsaturated fat8
ButterMonounsaturated fat1

How many empty calories did you eat? 

I had some lemons bars our new neighbors brought over 🙂 

I hope you found these case studies beneficial. If you’re curious about your fat intake, please contact me so I can learn more about how we can work together to help you live a healthier life and perform better. 

Photo by Maksim Shutov on Unsplash