Is breakfast really the most important meal of the day? Sure we’ve all heard the saying. But does it really ‘boost’ your metabolism? Does it help you burn calories, lose weight or stay slim?
Several observational studies have shown that habitual breakfast eaters tend to be slimmer than people who omit breakfast (1, 2). However, this finding is not consistent across all breakfast types. In the US National Health and Nutrition Examination Survey (NHANES III), those who regularly ate ‘meat and eggs’ for breakfast had higher daily energy intakes and BMIs compared to breakfast skippers; while those who ate a cereal-based breakfast had the lowest BMIs. This might suggest that leaner breakfast eaters are also more health conscious.
As for weight loss, according to the US National Weight Control Registry, which includes a group of successful dieters who’ve maintained weight loss of at least 30 Ib (13.6 kg) for one year or more, 78% regularly consume breakfast. It’s believed that energy intake at breakfast suppresses over-compensatory responses later in the day and helps regulate hunger.
However, many studies show that energy omitted due to skipping breakfast is not fully compensated for later in the day (3, 4, 5). There may be a transient increase in hunger (6) and calories consumed early lunch time (5; Figure 1a). But overall daily calories are lower when breakfast is omitted (3, 5)! Other studies show no change or an increase in total daily calories consumed in the absence of breakfast (7). It appears the science is divided.
As for ‘boosting’ metabolism – the bodily system that turns food into energy and regulates its utilization – the timing and frequency of meals appear to matter little. A recent randomised controlled trial (RCT) by the University of Bath demonstrated no significant differences in measures of metabolism (i.e. resting metabolic rate and diet-induced thermogenesis) when breakfast was consumed or omitted (8). Total intake of calories was higher for the breakfast group. However, habitual breakfast consumption was also associated with a higher level of physical activity.
Habitual breakfast consumption tends to coincide with other healthy behaviours, such as avoiding smoking, consuming less fat and alcohol but more fibre and micronutrients, as well as being more physically active (9, 10, 11). The study by Reeves et al. (5) showed that when breakfast was omitted the micronutrients iron and folate were reduced. It therefore remains unknown whether habitual breakfast consumption is a cause, an effect, or a feature of a healthy lifestyle.
THE SECOND MEAL EFFECT
There is emerging evidence that breakfast consumption may reduce post-meal blood glucose response to a succeeding meal (e.g. lunch). This is known as the “second-meal effect.” It has mostly been studied in response to certain carbohydrate-based foods with positive results in both healthy, normal-weight subjects and patients with insulin resistance and type 2 diabetes (12, 13, 14).
Animal studies suggest that this effect may be mediated by short-chain fatty acids (SCFA) (15, 16). These molecules are produced in the gut by healthy bacteria and can influence metabolic hormones, such as glucagon-like peptide-1 (GLP-1) (16). GLP-1 influences metabolism in a number of ways (16): 1) It reduces hunger and food intake. 2) It stimulates insulin release from the pancreas, which is required to regulate blood glucose. And, 3) it helps keep the pancreas healthy.
However, the type of food consumed is important. Fermentable dietary fibre and/or resistant starch appear to play a key role. Both dietary fibre and resistant starch are ‘resistant’ to digestion and arrive at the colon intake, where they can be utilised as an energy source for gut bacteria.
Foods that are rich in fermentable fibres and resistant starch include oats, legumes, beans, potatoes and rice (which have been cooked then cooled), unripened bananas, and other fruits and vegetables. Resistant starch constitutes a broad range of sub-groups, which exceeds the discussion here and will be covered in a future article.
The most common reasons for skipping breakfast include lack of time and concerns about body weight (1, 17). The science is yet unable to neither prove nor discredit the popular theorem that ‘breakfast is the most important meal of the day.’ Consuming breakfast may simply be a marker of a healthy lifestyle. It may also have implications for glucose and insulin regulation, which are yet to be fully understood.
Instead of obsessing over meal timing and frequency, eat when you’re hungry. If you’re hungry in the mornings, then eat breakfast. If not, then eat when you start to feel hungry. I truly believe that tuning in to our body is one of the best things we can do for our health.