"Lunching like a prince and dining like a pauper really is the key to keeping trim," the Daily Mail explains, reporting how evening meals should be light and post-dinner snacks avoided. This claim is unsupported by the findings of the research.
The study that the Mail based this story on involved mice. It found that normal mice were less ‘sensitive’ to insulin later in their day (hour 19 of 24). This can loosely be translated to mean that they would need less food at this time. However, mice that were genetically engineered to have no body clock did not show the same pattern of insulin sensitivity. These engineered ‘clockless’ mice also gained more body fat when fed an identical high fat diet to the normal mice.
This helps us understand how people’s body clocks work and how they may have a role in conditions such as obesity or diabetes. However, based on this study alone it is not possible to say what the ideal size or timing of the main meal of the day would be.
For now, the best advice remains to maintain a healthy diet, with calorie intake balanced with activity.
Where did the story come from?
The study was carried out by researchers from Vanderbilt University, Nashville, US. No sources of funding are reported. The study was published in the peer-reviewed scientific journal Current Biology.
The Daily Mail’s reporting of the study is poor. A single study in mice is not sufficient evidence to support the statement in the headline that timing of eating “is the key to keeping slim”. Also, the news does not mention physical activity, which is also likely to play a role.
What kind of research was this?
The research looked at the daily biological rhythm of the body (circadian rhythm). The researchers say that disruption of this rhythm increases the risk of:
- metabolic syndrome (a combination of risk factors for cardiovascular disease including high blood sugar, cholesterol and blood pressure)
- type 2 diabetes
They speculate that disruption of insulin (the hormone that regulates blood sugar levels) could play a role in this link. This laboratory research used mice genetically engineered to lack a functioning version of one of their ‘body clock genes’.
Researchers looked at insulin action and the physical activity patterns of these genetically engineered mice and what happened when they ate a high fat diet. They compared these ‘clockless’ mice to normal mice as well as to a group of normal mice who were exposed to constant light in order to disrupt their biological clock.
Humans have similar genes that control their biological clock, and changes in the normal pattern of exposure to light and dark (such as shift work) are also believed to alter our insulin secretion and increase body weight.
This type of animal research may further our understanding of how similar biological processes may work in humans. Further research in humans would be needed to confirm any findings.
What did the research involve?
The research included normal mice and mice genetically engineered to lack the Bmal1 gene that controls their body clock.
In one test, the researchers looked at the daily action of insulin in normal mice and those genetically engineered to be ‘without a body clock’. To do this they gave the mice a constant infusion of insulin throughout the day, at the same time as measuring their blood sugar levels.
Insulin tells the body’s cells to take up sugar and this lowers blood sugar levels. When the mice’s blood sugar became low, an infusion of glucose was given to keep blood sugar levels constant. By doing this, the researchers were able to tell how responsive the body was to insulin by how much glucose infusion was needed to keep blood sugar levels constant.
The researchers also looked at what happened when the genetically engineered mice had their body rhythm genetically ‘restored’. They then looked at what the effects were of feeding the two different types of mice – normal and ‘body clockless’ – a high fat diet for two months.
What were the basic results?
The researchers found that in the normal mice there was a normal daily rhythm in the action of insulin. They found that normal mice became more resistant to insulin (they needed less glucose infusion as their own blood sugar remained higher) at the 19th hour of their day. This was said to correspond with the middle of the day when they were less active.
However, it is not clear what time this corresponds to in humans. The lead study author is quoted in the press release as saying: “it is good to fast everyday... between dinner and breakfast”. This suggests that hour 19 for the mice would correspond with the middle of the night in humans.
The ‘body clockless’ mice did not show any alteration in insulin responsiveness throughout the day. When their body clock was genetically ‘restored’ they found that the insulin responsiveness of these mice was also restored to its normal daily rhythms.
When the normal and ‘body clockless’ mice were fed a high fat diet they found that the ‘body clockless’ mice gained a higher amount of body fat compared with normal mice, even though their food intake was the same.
The ‘body clockless’ mice were also less active than normal mice.
The researchers again found that genetic restoration of the body clock ‘rescued’ the body rhythms of the genetically engineered mice, returning them to normal. They then confirmed their theory that disruption of the daily rhythm makes mice prone to obesity by placing the normal mice under constant light conditions to disrupt their body clock.
They found that if these light-disrupted normal mice were fed a high fat diet for three months they gained more body fat than normal mice who were also fed a high fat diet but kept under normal conditions of 12 hours of light and 12 hours of darkness.
How did the researchers interpret the results?
The researchers conclude that their study demonstrates that there is a normal daily rhythm in the action of insulin.
They say that they show that disturbing this rhythm (for example, using the genetically engineered mice, or by altering light exposure of normal mice) alters the sensitivity of their bodies to insulin and makes mice prone to gaining weight.
In a press release issued by Vanderbilt University, lead study author Professor Carl Johnson, said: “That is why it is good to fast every day…not eat anything between dinner and breakfast.”
This animal research furthers our understanding of how the biological clock affects insulin levels, activity and weight gain in mice. The effects may be similar in humans, but this ideally needs to be confirmed in studies involving people.
It was interesting that normal mice were found to be less ‘sensitive’ to insulin around hour 19 of their day. This was when they were most inactive, meaning that their blood sugar remained higher. As a result they needed less sugar to maintain their normal blood sugar levels. This could loosely be interpreted to mean that they would need less food at hour 19 of their day.
If similar patterns were found in humans it could potentially mean that we need less food at the end of our day, when we are less active.
The researchers also showed that disruption of the body clock made the mice more prone to obesity, and it would be interesting to study people who do shift work to see if similar results are found.
Overall, the Daily Mail’s interpretation of the research is that having a larger lunch and smaller dinner will help maintain a healthy weight in humans. However, the current research cannot prove this, mainly because these findings in mice may not be directly applicable to humans, but also for other important reasons:
- the mice with disrupted body clock ate similar amounts of food to normal mice but were less active – so activity is also likely to play a fundamental role
- the researchers did not test what the effects of altering the food availability of normal mice at different times of the day would be
Obesity is a major health problem and the levels of obesity seem to be getting worse. More research is needed to help us understand these problems and how they could be tackled. For now, the best advice remains to maintain a healthy diet, with calorie intake balanced with activity. Read more advice about losing weight safely.
Analysis by Bazian
Edited by NHS Website
Links to the headlines
Daily Mail, 21 February 2013
Links to the science
Current Biology, published online February 21 2013