Understanding personal nutritional responses. Part 1: What happens when you eat?

In our previous blog posts, we’ve highlighted how understanding your individual responses to food can help you eat in a way that supports your health.

We’ve also discussed how responses to food vary wildly between people, and even identical twins can respond differently to the same foods.

But what exactly do we mean when we talk about responses to food?

To explain, we’re going to focus on the two most important energy sources in most of the foods we eat: fat and sugar.

How fat and sugar end up in the blood

Let’s take a moment to recap some high school biology. Every time you eat and drink, food and beverages make their way into your stomach where they are broken down by stomach acid and enzymes.

Then, it passes into your intestines, where more enzymes break down the carbohydrates, fats, and proteins in your food into smaller chemical building blocks, such as simple sugars from carbohydrates, triglycerides from fats and amino acids from proteins.

These small molecules pass through the walls of your intestines and eventually end up in your bloodstream.

Almost all the fat we eat is made up of triglycerides, and most of the carbohydrate we eat breaks down into a type of simple sugar known as glucose, so it’s not surprising that these molecules turn up in our blood in large quantities after we eat.

(A quick note on ‘sugar’: carbohydrates are made up of sugar molecules strung together into long chains. Glucose is the commonest carbohydrate building block in most of the foods we eat.

Chemically speaking, simple sugar molecules like glucose are different from table sugar, which is actually sucrose – a molecule made up of glucose and fructose joined together. So when we talk about measuring ‘blood sugar,’ we’re usually referring to glucose.)

A spoonful of sugar

What do blood glucose and triglyceride levels reveal about your metabolism?

When you eat, the levels of glucose and triglycerides in your blood increase. These fat and sugar molecules circulate until your cells take them up and either use them for energy or store them for later, reducing the amount of these molecules in the bloodstream.

Measuring how the levels of glucose and triglycerides in your blood rise and fall after eating helps us to understand how quickly your body releases the nutrients from food and how fast it uses them for energy or stores them once they are circulating.

How your blood glucose and triglycerides levels change after you eat, and how swiftly they return to normal is what we at ZOE describe as your response to food, or personal nutritional response.

If you respond poorly to food and the levels of glucose in your blood peak quickly and then crash, or remain high for a long time, you are more likely to gain weight.

People with unhealthy nutritional responses are also at risk of developing serious health problems like diabetes and heart disease

You spend most of your day digesting

Your body breaks down carbohydrates quickly, and glucose travels directly through the walls of your intestines and into your blood. As a result, your blood glucose levels increase rapidly, usually peaking at around 30 minutes after eating and returning to fasted levels after about 2 hours.

Blood sugar responses are usually measured first thing in the morning before breakfast, providing a baseline readout after fasting. 

Triglycerides also make their way into the cells that make up our intestinal walls, but are packaged into tiny particles called lipoproteins (‘chylomicrons’, if you want to get technical about it).

The process of getting these fat particles into the bloodstream and back out again is very slow, so your fat response takes up to 8 hours to rise and fall after just one single meal. 

Eating another meal before those 8 hours are up just adds more fat to the pile, driving up the levels of triglycerides in the blood even further.

The result of combining these different processing speeds means that our bodies are in what’s known as a post-prandial state for around 18 hours in a typical day as we break down and use food.

A graph showing typical blood fat and sugar rises over a full day
Typical blood fat (orange) and sugar (blue) responses over a full day.

The real meal deal

In the past, most research has focused on investigating how various food sources of fat or carbohydrate affect either our blood glucose or blood triglycerides. But no one eats meals made up of just fat or just carbohydrates.

Human diets vary hugely, mixing up a whole range of beverages, foods and nutrients. What’s more, our bodies can make triglycerides into glucose and vice versa, so the two are closely interlinked.

More recent research has used carefully standardized meals to investigate responses to foods and combinations of nutrients. Far fewer studies have examined how we respond to regular, real meals during our everyday lives. 

Here at ZOE, we understand the power of standardized meals, which is why our scientific test muffins are so useful. But we also appreciate that most people might not want to live on our muffins all the time, no matter how delicious we think they are.

We want to understand responses to food during normal life, so we can help everyone find the foods their body loves.

That’s why our PREDICT studies are designed to measure nutritional responses as participants eat, drink, exercise, sleep and go about their normal daily lives.

Your responses to food are as unique as you are

Our food, eating habits, bodies and lives are complex and varied, so it makes sense that our responses to food are too.

Your blood sugar and fat levels are affected by a huge range of things including what you ate during your last meal, your genetics, how stressed you feel or how much sleep you got last night. And, of course, there’s a major influence from the microbiome – your personal collection of gut microbes.

Your responses to food are as unique as you are, and we believe that understanding your body is the key to finding the best way to eat to maintain your health and manage your weight.

Our next few posts will go into more detail about how your blood glucose and triglyceride levels change when you eat, how we measure them, and the implications for your health, so watch this space.

In the meantime, sign up to our mailing list if you’re interested in taking part in our research or want the latest updates.

Content on this blog is licensed under a Creative Commons Attribution-NonCommercial-NoDerivatives 4.0 International licence. This means you’re free to reproduce it without any changes as long as you attribute ZOE and link back to the original post, but you can’t charge people to read it.

Recent articles