Crossing the threshold: How much fat is too much?

February 2, 2021

Although it’s had a bad rap over the years, we all need to eat fat to stay healthy. 

Fat contains essential fatty acids (EFAs), which play a vital role in many of our bodily functions, including building cells, proper development of the brain and nervous system, eicosanoid production (hormone-like chemical messengers) and more. We can’t make our own EFAs, so we have to get them from food. Fat is also important for helping us to absorb fat soluble vitamins A, D and E, and is a useful source of energy.

Beyond the roles fat plays in our body, it also makes the food we eat taste great! Fat carries flavor, it excites our palates, and provides texture and mouthfeel to our food. 

Not all fats are the same, and there are differences in the type and quality of fats in different foods. But it’s not just the quality of fat you eat that’s important - the quantity matters too. 

Our research has shown just how unique our responses to the fats in the meals we eat are. But how much fat is too much?

We take a look at how blood fat levels change after eating, what happens if you eat a lot of fat in a short space of time, and how you can understand your own unique fat metabolism. 

Facts about fat metabolism

  • Fat is an important nutrient that we need to stay healthy
  • Your body removes fat from your bloodstream more slowly than sugar
  • It can take up to 6-8 hours to process fat in your blood after a fatty meal
  • As a result, your blood fat can rise continuously throughout the day
  • Prolonged, unhealthy blood fat responses can increase dietary inflammation and if repeated often enough, contribute to negative health outcomes over time
  • Everyone has a unique response to fats, which is why understanding your blood fat responses is key to helping you make the best food choices for your body 

Find out more about fat in our article about macronutrients.

Blood fat accumulates throughout the day

Your blood sugar levels rise and fall after eating, resulting in peaks throughout the day.This is a normal, healthy response to carbohydrate-containing meals and usually happens reasonably quickly (depending on what you’ve eaten, of course). This means that blood sugar levels often return to baseline before you eat your next meal or snack.

When you eat foods that contain fat, the fat travels into your bloodstream as molecules called triglycerides, packaged into little packets known as lipoproteins. These triglycerides are then taken up by the cells of your body, where they are used for energy or stored for later. 

Triglycerides move out of your blood much more slowly than sugar, so your blood fat levels may still be raised when you eat your next meal.

This graph shows typical blood fat (light pink), blood sugar (dark blue) and insulin (coral) responses over the course of a day:

As a result, if you continue eating fatty meals throughout the day, your blood fat levels may build up with each meal. This means you end up with an elevated triglyceride level that can stay elevated for a long time. 

Repeatedly experiencing these prolonged, elevated blood fat responses can trigger dietary inflammation, which is a term that we use to describe all of the unhealthy effects caused by eating the ‘wrong’ foods for your body. 

One of the processes involved in dietary inflammation is lipoprotein remodeling, where the lipoprotein particles in your blood change size or composition, making them more likely to cause damage to your arteries. 

These unhealthy responses have been linked to long-term health problems, including an increased risk of heart disease and strokes. 

Finding your fat threshold

It’s not all bad news. Our research shows that most of us can eat a certain amount of fat before getting into this unhealthy state - a boundary we call your fat threshold. 

Staying below your fat threshold means your body can process most of the triglycerides from your blood before you eat again, helping your body remain within healthy blood fat levels.

So how do you know your fat threshold?

Our research has shown that where your fat threshold lies depends on what you eat and who you are.

In our PREDICT studies, we measured the participant’s triglyceride levels after eating a standardized meal consisting of a muffin with a specific amount of fat. 

We found that everyone responds to fat differently, and blood fat levels can vary wildly between people, even after eating identical foods.

This graph shows blood fat measurements from 1,000 participants who took part in our PREDICT 1 study. These measurements were taken at regular intervals (over 6 hours) after participants at identical breakfast (at 0h) and lunch (at 4h) meals. 

The red line represents the mean response, blue indicates the median response, and each of the black lines represent an individual's blood fat response.

As you can see, our research shows that everyone has a different response to the fats in our food. This also means that each of us has a different fat threshold. 

How much fat you should eat over the course of the day depends on your unique metabolism. 

Our ZOE scores help you understand your unique fat response

To find your own fat threshold, you need to understand how your body responds to the fat in your food and how quickly you remove triglycerides out of your bloodstream. 

Our ZOE test kit contains the same standardized muffins as we used in our PREDICT studies, with specific amounts of fat. After eating these muffins, we ask you to use a finger prick blood test 6 hours later to collect a blood sample. 

We use these blood samples to measure your blood fat responses and how well your body processes fats after you eat. This gives us an idea of how you process fat and helps us find your fat threshold.

Using this data, you’ll receive personalized scores for thousands of foods and meals through the ZOE Insights app to help you decide which foods suit your body best. 

For each food, meal, and day, the app gives you a score for the food you eat. One part of the score includes whether you are likely to be hitting your personal fat threshold depending on the food you have eaten, the quality of the fat sources in your meal, and your unique metabolism.

If you go above your fat threshold, you will notice that your scores drop. Although we believe there are no ‘bad’ foods, maintaining a high day score most of the time can help you avoid prolonged blood fat peaks and improve your long-term health.

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