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Feeling Hungry All The Time? Scientists Have a New Explanation For What's Going On

17 APRIL 2021

The interplay between blood sugar and appetite appears to be more complex than scientists realized, with new research showing that glucose levels in the blood even several hours after eating can still have a pronounced effect on how hungry people get later in the day.


Specifically, the new findings reveal that some people are prone to experiencing 'sugar dips' up to four hours after eating their last meal – a delayed glycemic response that turns out to be a more accurate indicator of appetite (and energy consumption) than glucose levels following meals.

"It has long been suspected that blood sugar levels play an important role in controlling hunger, but the results from previous studies have been inconclusive," says nutrition scientist Sarah Berry from King's College London.

"We've now shown that sugar dips are a better predictor of hunger and subsequent calorie intake than the initial blood sugar peak response after eating, changing how we think about the relationship between blood sugar levels and the food we eat."

In the study, the team sourced data from PREDICT (Personalised REsponses to DIetary Composition Trial), an ongoing nutrition research project involving several universities across the world, in collaboration with commercial health science company ZOE, co-founded by genetic epidemiologist Tim Spector from King's College London.

The researchers examined blood sugar responses and other indicators from 1,070 participants in the UK and the US, who ate standardized breakfasts, followed by freely chosen meals for the rest of the day, with a no-eating window set for three hours after breakfast.


During this regimen, which lasted for two weeks, the participants continuously wore blood glucose monitors, designed to keep track of their blood sugar levels throughout the study, and recorded when and what they ate in a phone app, along with reporting their levels of hunger during the day.

The dataset, which ultimately collected information on tens of thousands of meals consumed by the cohort, indicated that the sugar dips some experience hours after eating – aka postprandial [post-meal] glucose/glycemic dips – are significantly associated with both appetite levels and energy intake in healthy individuals, under what can generally be regarded as real-world conditions.

"Our discovery that the size of sugar dips after eating has such a big impact on hunger and appetite has great potential for helping people understand and control their weight and long-term health," says senior author and genetic epidemiologist Ana Valdes from the University of Nottingham.

According to the researchers, links between blood glucose levels and appetite have been known since the 1950s but have generally fallen out of favor among scientists due to mixed evidence on how blood sugar availability actually suppresses feelings of hunger. Much of the current research focuses on chemical signals' role, like the protein leptin and other so-called hunger hormones.

But glucose is still very relevant, the team says, with the results showing that people who exhibited big blood sugar dips experienced a 9 percent increase in appetite, in addition to eating their next meals roughly half an hour sooner, and ultimately consuming over 300 calories more during the day than participants who experienced only slight drops in glucose levels.

What's more, these sugar dips, with a low point occurring about three hours after the previous meal, were as good a predictor of subsequent energy intake as the participants' self-reported hunger.

While the researchers acknowledge a number of limitations in their study – including self-reported results, and the fact that appetite hormones themselves were not measured in the experiment – the team says their results provide quantitative evidence of the links between glucose dynamics and appetite and energy intake.

For many, it's an insight that might help them to understand part of what it is that's driving their hunger – and potentially do something about it to make a life-changing difference.

"Many people struggle to lose weight and keep it off, and just a few hundred extra calories every day can add up to several pounds of weight gain over a year," Valdes says.

The findings are reported in Nature Metabolism.