Nitty Gritty on Fat Intake Part 2 - What happens to fat?

Last week we covered body-weight regulation and how our bodies preferentially burn excess protein and carbohydrates for energy.  It leaves us with the nagging question of "what happens to fat"? Do we need to eat extremely low amounts, can we have fat and still lean out, what happens if we gain or lose weight? Ultimately, we need to find out what happens when we ingest dietary fat and how our total calories impact the ultimate changes in our body-fat levels.

What happens to fat?

If we eat more carbs and protein and burn more of each, do we do the same with fat?  Interestingly, our bodies don’t regulate fat oxidation as strictly.  Increasing fat intake does not result in an increase of fat oxidation. Damn.

Any time you are eating in a calorie excess from protein or carbohydrates, you might burn more of both, but they are in fact sparing fat, leading to fat storage. Since increased fat intake does not mean more oxidation of fat, it obviously benefits us not to over-eat carbohydrates or protein alongside excess dietary fat. In most cases the excess calories stored as body fat will come from dietary fat.

The next question might ask how we increase fat oxidation, then?  Surely there must be scenarios where we can burn more fat. We can increase fat oxidation through exercise, so that’s good to hear! If you expend a few hundred calories during a training session, your rates of fat oxidation will go up. But we can also increase fat oxidation by simply gaining weight.

If you over-eat (whether it’s fat protein, carbohydrates or fat) without changes in activity, eventually you’ll gain weight from a mix of fat and muscle, mostly fat. As you gain body fat, your fat oxidation increases because you have larger fat cells.  Kind of like how with larger muscles you use more protein. In a way, body weight gain is a regulatory mechanism to increase energy expenditure and fat oxidation to match excess dietary fat.

Here’s how it works:

  1. A 150lb man is weight stable with a fat intake of 70g per day
  2. If he increases fat intake by 20g, he still only oxidizes 70g daily
  3. The extra 20g of dietary fat not oxidized is stored as excess body fat
  4. When body fat increases to a satisfactory level, fat oxidation will now match the extra 20g consumed

Essentially, he’ll gain body fat until his total body fat is oxidizing that 90g per day (70g plus 20g). Once he matches oxidation to intake, body fat gain will stop. Schultz et al concluded that an excess of 20g dietary fat daily would lead to increase of 22lb body fat before oxidation matched intake.

Being sedentary will really make this happen.  If you have a lot of muscle and stay active and exercise, you might be able to oxidize off a good amount, leading to a smaller body fat increase. It doesn’t mean that you won’t gain fat though which is why just adding exercise doesn’t necessarily mean larger weight loss.

Weight Gain

Gaining body fat will of course result in gains in lean body mass as well.  With more weight to support, you will increase the cross-sectional area of your muscles.  Sumo wrestlers have the highest fat free mass indexes on the planet yet they are morbidly obese and don’t engage in resistance training.  Having huge levels of body fat though (and they certainly do train hard) result in large amounts of lean mass gain as well.

Understanding this is critical to understanding that larger people (yes even those over-weight) have higher calorie needs.  Being larger with more organ mass, more weight to move, more surface area for heat loss and likely greater muscle mass result in higher energy needs. You really can’t be 250lbs and maintain your weight on 1000 calories per day. An individual who is over-weight or obese is likely consuming the calories that support that weight.

You can start to see how yes, total calories obviously matter for weight loss or gain.  Even though we oxidize more protein or carbohydrates if we eat more, it doesn’t mean that we won’t be storing excess dietary fat calories as body fat.  Overeating is still overeating and will lead to some sort of weight gain.

Weight Loss

This holds true for weight loss as well.  It doesn’t matter that dietary fat is stored more easily as body fat if you are in a calorie deficit because you’ll still be in need of fat for energy.  It’ll be oxidized off to meet energy needs. It also means you can lean out on a low-fat but higher-carb diet. The approach that works best for you personally and you find the most satiety with is the optimal one.

Of course, protein needs to monitored for this to happen optimally.  If you’re in a calorie deficit you need more protein; as your body is looking for other fuels to burn as energy it WILL pull some from protein.  So, in a deficit, protein needs go up.  In a surplus, where there is abundant energy, there is no real need to pull energy from protein as there is plenty from carbohydrates and/or fat to go around.

Personally, I do like to keep carbohydrates as high as possible when dieting simply because they can help contribute to good training sessions, nice pumps and less brain fog.  If you have real issues with insulin sensitivity then a low-carb approach might be more optimal but for the average individual either one will do. Someone who is more active will probably get more bang for their buck with more carbs while someone less active won’t need as many. Either way, in a deficit you don’t have a lot of calories to work with so it’s not like you’d be eating 10g fat per day but 350g carbs!  Fat and carbs both need to go down, the degree of each is individual.

What’s Practical?

The conclusions here are that yes, dietary fat is more easily stored as body fat.  The implications for this are prioritizing carbohydrates when looking to gain muscle, engaging in a ton of activity or exercise and when you have a lot of muscle mass. You’ll probably have an edge with more carbohydrates because you have multiple pathways to use them optimally.  You simply won’t need as much fat in this scenario because carbohydrate needs are more pressing.

Your fat needs will really center more around your total body fat.  If you seem to be weight stable and healthy at a current fat intake then there isn’t much benefit in prioritizing excess dietary fat while trying to gain muscle or participating in high-intensity sport activity.  I will say that practically speaking, at a certain point eating only more carbs becomes difficult and you’ll probably need to add some additional fat simply for the calories.

When it comes to fat loss, you’re more looking toward energy expenditure to determine carbohydrate needs.  In this scenario, you don’t want carbohydrates to be so low that it impacts your training and recovery. Ideally, you’d scale carbohydrates toward activity and then adjust the remaining calories from fat.

When you’re able to consider the importance of each macronutrient and how each impacts training, recovery and of course preference, it’s much easier to choose an approach without worrying about what’s cool or exciting.

Step Away With This

In most cases, protein and carbohydrates will be used for energy, even when eaten in excess.  This leaves dietary fat as the preferential macronutrient to be stored as body-fat.  But if you are in a calorie deficit, you’ll simply burn off that stored body-fat to meet energy demands.

The ratios of your macronutrients will have a huge impact on recovery, performance, satiety and digestion but the overall calorie intake will ultimately determine weight loss or gain. The most practical advice is to set your protein and calories to match your goal, then set your amounts of carbohydrates and fat based off how you subjectively feel, how well training/recovery is going and what leads to the best satiety and adherence outcomes.