Episode 153 – Does Meal Timing Affect Fat Loss?

Key Topics Covered

Clock on the table with food.

Whether meal timing can affect fat loss can be approached from both the theoretical side of things and also the practical side. 

We will start with theoretical information first, largely looking at if there are differences in results when total intake is matched, to isolate meal timing as a variable. Then we will discuss the practical side.

Insulin

  • Insulin sensitivity is higher in the morning.
  • Insulin secretion is better in the morning too -research has found improvements in beta-cell function (the cells that produce insulin).
  • We also see shift workers as an extreme example of this where blood glucose levels and insulin are often affected. However, the impact of sleep is a huge variable here.
  • Although this is relevant from a metabolic standpoint for risk factors such as type 2 diabetes, it doesn’t play much of role in the specific question of whether it affects fat loss. Insulin resistance at most plays a small role when all other factors are equated for. 

Does Breakfast Play a Role?

Healthy Breakfast Platter

Many people will argue that having breakfast is an important aspect of fat loss. The logic that is often used here is that:

  1. Eating breakfast can increase energy expenditure throughout the day by making you more energetic.
  2. Eating breakfast “kick-starts the metabolism”.
  3. Eating late in the day increases fat storage since you aren’t “burning it off”.
  4. Eating breakfast will mean you aren’t as hungry later in the day.
  • We actually have previously recorded a podcast on this topic looking at these different arguments, so if you want a deeper dive see episode 105. 
  • But to cover this simply:
  1. Breakfast doesn’t noticeably increase energy expenditure. There could be individual variation with the effect on activity levels, but it definitely doesn’t “kick start the metabolism”.
  2. We are always burning calories, even while sleeping, so eating late in the day doesn’t mean we won’t burn it off. When it comes to weight gain or loss, we are looking at calories in versus calories out over days, weeks and months. If you are eating in a caloric deficit, it doesn’t matter if you have breakfast or not. That in isolation won’t move the needle one way or the other. 
  3. From a hunger perspective, research actually shows that those who eat breakfast on average have slightly higher calorie intakes. But it’s also individual. For some people adding breakfast will help from this perspective. For others it won’t. 
  • The crux of all of this is that there isn’t anything magical about breakfast specifically that makes it important or unimportant for fat loss. 

Thermic Effect of Food in the Morning

  • Outside of the insulin aspect, the closest thing to a “magical” factor is that some research has found that the thermic effect of food is higher in the morning than in the evening.
  • The most cited study on the topic only had 14 participants, but it was a crossover design and they found the thermic effect of food was ~50% lower in the evening than in the morning.
  • This effect likely isn’t significant enough to adjust your day specifically for this reason though. 

Small Frequent Meals to “Stoke the Metabolism”

Small meals on a table.

  • Back in the day a lot of people would say that small frequent meals would speed up metabolic rate.
  • This is pretty easy to debunk from a few angles.
  • The first one is simply looking at the research. A review on the topic found no noticeable difference in energy expenditure. That’s simple enough. They also highlighted flawed thinking that some people use based on short-term studies looking at the thermic effect of food. Over larger time frames, calories burned through TEF are more linked to total intake rather than frequency.
  • The second way would simply be to look at the other extreme, which is intermittent fasting.

Intermittent Fasting

  • Intermittent fasting gets the same results from a fat loss perspective when total intake is matched.
  • Heaps of research has found this. 
  • But using a specific example that takes this a step further, a study from 2017 looking at alternate-day fasting vs continuous energy restriction with calories matched over a 6-month period found similar fat loss results in both groups.
  • The alternate-day group consumed 25% of calorie needs on fasting days and 125% on other days. The other group consumed a consistent 75% of their maintenance.
  • If meal frequency in isolation noticeably affected energy expenditure, it would be evident in studies like this, but that hasn’t been the case.

Othe Research

  • It’s worth noting that the practical aspect of this topic. Almost every randomized controlled trial that has been done on intermittent fasting has found significant weight loss.
    • A smaller eating window often results in a reduction in caloric intake.
    • It is important to note that this will not be the case for everyone.

Protein Distribution and Impact on Muscle vs Fat Ratio

Man measuring bicep.

  • If you focus on acute research looking at muscle protein synthesis it can make you believe that it is really important to spread out protein intake across the day.
  • We’ve spoken about this many times on the podcast, but when total protein and calorie intake is appropriate, people retain muscle quite well in intermittent fasting research. 
  • We don’t have much research looking at muscle growth in IF, since people consistently end up in a deficit.
  • If people lost more muscle vs fat with different meal frequencies, this would have an indirect impact on fat loss. But that’s not something we see.

Practical Standpoint

  • All of that is theoretical, the practical side of this topic is more nuanced.
  • Meal timing has a huge role to play in appetite management.
  • Individual approaches are needed here. 

Grazing vs Intermittent Fasting

  • For example, if somebody is constantly grazing across the day, they likely end up consuming more calories than desired. 
  • On the flip side, while almost all research on IF has found people lose weight with that approach, there also is the classic example of people missing breakfast and being starving later in the day and that leading to higher calorie intake.

Eating Windows

  • Overall, some attention should be paid to eating windows. 
  • Research on animals has consistently found that extended eating windows can be an issue for longevity. There’s not much reason to believe that holds true in humans, but I still wouldn’t take it to an extreme.
  • Beyond that, having an eating window that is >14 hours often makes it difficult to consume fewer calories vs say 10 hours. That’s not time-restricted eating, but it is simply avoiding having a massive eating window.

Summary of Meal Frequency

  • There is no ‘one size fits all’ for this one.
  • Experiment with meal frequency, timing and eating windows to see what works best for you.
  • This could be:
    • 3-5 eating occasions across the day.
      • Timed roughly equally apart or adjusted around based on when the desire to eat and hunger is higher.
      • Eating window of 8-12 hours,

Why Does the Research Look So Mixed?

Food with magnifying glass.

  • This is hard to answer because there are so many reasons.
  • The main one is because of the practical considerations.
  • Example: If we look at research on skipping breakfast – are calories matched? If the calories are matched, it makes it better to identify if breakfast plays a specific role independent of calorie intake.
  • If intake is ad-libitum and calories aren’t matched, it makes it more relevant to the real world but means we can’t draw strong conclusions about what would happen if calories were matched.
  • Sometimes there are small sample sizes. Sometimes random chance occurs. It’s also bold to assume that in all studies the calories are set up perfectly.
  • Example: if you gave all participants the same calories, that won’t make sense because they all have different needs. But if you give them different calories, how do you know for sure you have given them all appropriate calories for them as an individual within a small margin of error for the duration of the study?
  • This is why it makes sense to look at the body of research as a whole rather than individual studies.

Summary

From a practical perspective, there is a lot to consider, but it is not a ‘one size fits all’. It’s going to take some experimenting to find what works best for you.

Relevant Blogs / Resources

Podcasts:

Research:

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