Does when we eat affect weight loss?

Eating late at night

Eat breakfast like a king, lunch like a prince and dinner like a pauper – advice originally given by Adelle Davis, a well-known nutritionist in the 1940s and 50s. This idea about the importance of meal timings and when to eat the most food has been around for a number of decades now, and despite Davis' advice at the time not necessarily being backed by solid scientific evidence, she may well have been onto something.

Research into when we eat the majority of our calories, does suggest that a bigger intake earlier in the day could help boost weight loss. One study split 93 overweight women into two groups – one group ate a 1,400 calorie diet consisting of 700 calories at breakfast, 500 calories at lunch and 200 calories at dinner, and the other ate a 1,400 calorie diet consisting of 200 calories at breakfast, 500 calories at lunch and 700 calories at dinner (Jakubowicz et al., 2013). The diets were followed for 12 weeks, and nutrient content and mealtimes were consistent across both groups.

At the end of the 12 week study period, those in the higher calorie breakfast group had lost significantly more weight than those in the higher calorie dinner group. These findings suggest that eating more calories earlier in the day can boost weight loss regardless of overall energy intake.

This effect is thought to be due to our natural circadian rhythms (our body's natural cycle over a 24-hour period which responds to light and dark) and when our body is most geared up to digest food. It's been shown that our glucose tolerance and insulin sensitivity is higher in the morning when we need to refuel after overnight fasting (sleep), and decreases as the day goes, meaning our body is not as efficient at metabolising foods later in the day.

Skipping breakfast

Breakfast is the most important meal of the day – so they say! But is it true? Eating a well-balanced breakfast is certainly a good way to kick off the day and a great opportunity to get some all important nutrients into our body such as fibre and protein. But what happens when we skip it and wait until lunchtime before eating?

Some research has shown that this habit impacts on our circadian rhythms by delaying an increase in our core body temperature at the start of the day, which can be associated with our metabolism firing up for the day (Ogata et al., 2020). This highlights a relationship between when we eat and our body's natural rhythms and processes – but doesn't necessarily mean skipping breakfast will result in weight gain.

It's long been believed that people who eat breakfast regularly tend to have a lower body weight than those who skip breakfast. There may be some research to support this notion, but it's mostly correlational evidence and so doesn't prove cause and effect. It may be that people who choose to eat breakfast are generally more mindful about healthy eating and therefore eat a healthier diet overall – which is the real reason for their lower weight, as opposed to it being simply because they eat breakfast.

A meta-analysis which looked at the results from 13 studies investigating the association between breakfast eating on total energy intake and body weight, concluded that eating breakfast was not associated with a lower body weight or a smaller total energy intake across the day (Sievert et al., 2018). These findings suggest it's not as simple as eating breakfast equals better weight loss, but that our overall diet and energy intake across the day is of most importance.

Regular eating patterns

Research suggests that following a regular eating pattern is beneficial to our health, compared to irregular eating behaviour. One study measured the effect of eating six regular meals per day, compared to eating a mixture of three, six or nine meals across different days, on markers like glucose response, the thermic effect of food, insulin response and hunger hormone levels (Alhussain et al., 2016).

What the researchers found was that a regular eating pattern was associated with a greater thermic effect of food and increased insulin sensitivity after meals, which suggests following a regular eating pattern may help our body handle the foods we eat more efficiently. Although further research is needed in this area, the findings that irregular eating patterns decrease the thermic effect of food could mean that irregular patterns may lead to increased weight over time, due to lower energy expenditure.

The research suggests that regularity is important, but doesn't explore exactly which pattern of eating is best. Eating 3 meals, 6 meals or 9 meals per day could all be absolutely fine, providing you are consistent in this eating pattern over time.