Does when you eat matter as much as what you eat?

December 3, 2020

When you eat matters as much as what you eat

We’re all used to the idea that what we eat is important for our health. But you might not think that when you eat matters quite as much.  After all, an apple has the same number of calories, macronutrients, and food matrix whether you eat it in the morning or the evening, right?

Well, it's not quite that simple. Data from our PREDICT studies shows that eating the same foods at different times of the day can actually have a big impact on how your body responds to them. What’s more, what you’ve already eaten can have a knock-on effect on your next meal.

We asked our expert Dr. Sarah Berry, lead nutritional scientist at ZOE, to explain more about meal timing, blood glucose control, and how understanding your unique biology can tell you the best to eat.

Our bodies are on a 24-hour clock

Our internal body clocks regulate virtually every process in our body, including our hormones and digestive cycles. As a result, there are particular times of day when our bodies are more prepared to utilize our food than others.  

“We’ve known for decades that when you consume your food affects how you respond to it,” confirms Sarah. 

So when is the best time to eat? 

Most people eat three meals per day and a few snacks, with their main meal in the evening. But is this the right pattern to stay healthy and get to your best weight? 

When should you eat? It depends on your unique biology

You may have heard the old saying, “Eat breakfast like a king, lunch like a prince, and dinner like a pauper,” meaning that you should eat your largest meal of the day first, with a smaller lunch and an even smaller dinner. So is this really true?

Studies measuring the blood sugar responses of people eating set meals in the morning and the afternoon show that, on average, people tend to have better control over their blood sugar levels in the morning compared with the afternoon or evening.  

However, these averaged results mask a huge amount of variation between individuals.

In our PREDICT studies, we looked at how individuals responded to food and how their blood sugar control varied throughout the day. The results show that one-size-fits-all advice on meal timing might not work for everyone.

“We found that while people have better responses to carbohydrates in the morning on average, there is huge variability between individuals,” says Sarah. 

“Some people have better control over their blood sugar in the morning compared with the afternoon in line with the average, but it’s not the case for everyone, with some responding better in the afternoon.”

This means that for some people, eating their main meal at dinner time may be better for their health, weight and metabolism than eating a big breakfast. 

“We find that the difference between morning and afternoon is particularly significant for younger people, perhaps because metabolic control diminishes with age so older people may not have good control over their blood sugar levels whether it is morning or afternoon,” Sarah explains.

What you eat for breakfast changes your responses to lunch

The differences in nutritional responses in the morning compared with the afternoon may be down to more than just time of day. How your blood sugar levels change after you eat also depends on what you ate for your previous meals. 

“We did a follow-up study called PREDICT-Carbs, which was specifically designed to look at how the time of day and meal sequence affects responses to food,” Sarah says.

“We found that meal sequence - what you had eaten in previous meals in terms of fat and carbohydrate content -  had a really big impact on nutritional responses,” says Sarah. 

In one experiment, everyone ate different 500 calorie meals for breakfast, and then they ate the same standardized meal for lunch. 

“Not only did we find that the responses to the identical lunches were highly variable, as with our other PREDICT studies, they also depended on what people had eaten for breakfast,” says Sarah. 

Understanding your unique biology can tell you what and when to eat

“We are just starting to unravel exactly how much variability there is in responses to food depending on the time of day,” says Sarah.

“On average, we know people respond far better to carbohydrates in the morning, so you may want to try and limit highly accessible carbohydrates from lunchtime onwards. If you like white bread, for example, it may be better to eat it at breakfast time rather than dinner.”

“But we have seen huge variability in how people respond to carbohydrates, with some responding better in the morning and some better in the afternoon, so the only way to really know the best time for you to eat is by understanding your unique biology.”

So how do you know whether a big breakfast is best for you, and what you should eat to set your metabolism up for the day? 

The answers lie in understanding your own unique biology. Our ZOE test kit has everything you need to measure your metabolism and get personalized recommendations for thousands of foods that will work with your body, not against it.

Top tips for meal timing

  • A 24-hour internal clock regulates our hormones and digestive systems.
  • Responses to food vary with time of day, and most people have better blood sugar control in the morning compared with the afternoon.
  • As a result, some people may benefit from eating a larger breakfast and a smaller dinner.
  • But there is enormous variability in responses to food with the time of day. Some people have similar responses all day, while others respond better in the afternoon.
  • Eating your biggest meal when you respond best may help protect your metabolic health and aid weight loss. 

Find out more:

Discover your unique biology

Understand how your body responds to food with ZOE

Take the first step