The weirdest dietary advice offered up so far this year has to be the fear-mongering about breakfast. One writer on this site has linked it to insulin resistance, type-2 diabetes, obesity, heart disease and cancer. That’s a lot for one meal to accomplish. Fortunately for those of us who enjoy breakfast, these claims are, in my view, based on bad science.
Central to the argument is the idea that randomised controlled trials (RCTs) are a superior form of evidence when it comes to studying diet and disease. As others have so eloquently argued, this is not necessarily the case. RCTs, in which subjects are randomly assigned to different groups, are limited by small sample sizes, limited follow-up and inability to blind diet treatment – people can see what they’re eating. They often tend to recruit subjects who are already unwell, further limiting their generalisability. Cohort studies, which gather data about individuals’ habits over a longer period of time, may provide a more robust insight.
Given that RCTs may not be all that, I propose we look past the small, extremely short term and frankly outdated work that has served as the basis for the criminalisation of breakfast, and look instead to studies with large sample sizes and long periods of follow-up. What insight do long-term cohorts give us into the relationship between breakfast and disease?
The Nurses’ Health Study is a large prospective cohort which studied the eating patterns of over 46,000 women, with a follow-up period of six years. After adjustment for confounding variables, the researchers from Harvard University found that frequent breakfast consumption appears to have a protective effect against type-2 diabetes, with women who consumed breakfast seven days a week having a 20 per cent lower risk compared to irregular breakfast eaters. This relationship was true even after adjusting for BMI.
Regular breakfast eaters were also leaner despite eating more calories, were more physically active, ate more fibre, and overall had healthier diet patterns that non-breakfast eaters (remember the relationship between breakfast and type-2 diabetes remained after these things were controlled for).
Likewise, an analysis of almost 30,000 men in the Health Professionals’ Follow-up Study, with a 16-year follow-up, found that men who skipped breakfast had a 21 per cent higher risk of type-2 diabetes — this relationship was true after stratification by BMI and diet quality.
Of course, cohort studies can’t prove a cause and effect relationship, but they at least suggest a positive relationship between breakfast consumption and health. Breakfast is far from a dangerous meal.
If it’s mechanisms you’re after, the emerging chrononutrition literature points to fascinating animal and cell studies, as well as (albeit limited) promising human studies.
Chrononutrition looks at what we eat in the context of our circadian rhythm – that is, the body clock according to which every cell in our body operates. It investigates how the timing of meals might affect the development of disease.
Breakfast is believed to set the time of the circadian clock, amplifying the genes that keep circadian rhythm within tissues and orchestrating metabolic activity. Skipping breakfast, meanwhile, is believed to reduce these signals and lead to circadian misalignment, putting the host at greater risk of metabolic disease.
Indeed, there is a compelling literature that skipping breakfast leads to weight gain, obesity, and metabolic abnormalities such as increased triglycerides and LDL cholesterol, fasting glucose, and reduced insulin sensitivity. One potential explanation for this is that circadian misalignment increases ghrelin expression. Ghrelin is a powerful orexigenic and may lead to overeating.
Night eating syndrome (where there is a time-delayed eating pattern) is associated with increased weight. Researchers believe that eating late and skipping breakfast leads to weight gain and obesity. One reason for this may be an insufficient satiety function. Clock genes control the satiety (or fullness) hormone leptin, and circadian misalignment causes a reduction of leptin in the blood stream throughout the day.
But that’s not the whole story. Another piece of the puzzle concerns dietary induced thermogenesis (DIT) – that is, the rise in body temperature we experience after we eat. This is caused by the energy we spend digesting, absorbing and assimilating food. We know that DIT is under circadian control, so it’s highest in the morning, and tapers off throughout the day. Scientists hypothesise that this could (at least in part) account for why people who skip breakfast don’t necessarily lose weight, especially if they eat more later in the day when their metabolism is effectively slower.
A study that nicely illustrates this placed obese women on an isocaloric diet, where calories are split equally between fats, proteins and carbohydrates. They were split into two groups: high calorie breakfast/low calorie dinner versus low calorie breakfast, high calorie dinner. Those in the high calorie breakfast group had better insulin sensitivity; they also lost more weight and had smaller waist circumferences than their low-calorie breakfast counterparts.
Recent literature in the area of intermittent fasting has shown promising results in terms of blood glucose control and other metabolic markers of health. But intermittent fasting doesn’t require skipping breakfast. In fact, I’d argue that a fast (as much as 12 hours in some people) can be built into your day without much difficulty — it’s just the period between dinner and breakfast. You don’t need to resist hunger, either: if you are hungry it’s an indication that you have fasted long enough and indeed there is evidence to suggest that responding to initial signs of hunger can improve glucose control.
It makes very little sense to vilify breakfast. Fibre intake in Britain is the real criminal here – currently we eat an average of 18g of fibre per day, just over half of the 30g a day recommendation. Breakfast provides an important opportunity to get fibre and other key nutrients into our diet. Blanket advice that we should eliminate breakfast may raise the risk of nutrient deficiencies.
Let’s be clear, there is far more evidence supporting the role of breakfast than there is linking it to disease. Whether you’re a breakfast person or not, let’s stop the scaremongering and talk about how we can improve the quality of breakfast.