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Time of eating influences health – PART 2

Watch Professor Alex Johnstone discuss what, when and how we eat influences our health and longevity.
ALEXANDRA JOHNSTONE: What do we know now to longevity and fasting? So fasting is, of course, an age-old practise that has been described in many religious texts and requires calorie restriction of various durations and formats. Now, I’ve pulled together some of the common types of formats of fasting that I’ve come across. One of the most popular ones just now is time-restricted feeding, which we’ll look at in a little bit more detail, where you restrict your eating, for example, to only 10 hours a day. And that would be perhaps even modified to the 16/8 plan where you only eat during eight-hour window and fast for the rest of the day. Or that could be 12 over 6 plan.
Only eat between noon and 6:00 PM. The Warrior Diet. That’s to mimic the eating habits or so-called habits of warriors in history where you fast for 20 hours. You consume foods only in a four-hour window. There’s One Meal a Day Diet, which has got the acronym OMAD. where you eat a large meal in a one-hour window and fast for the rest of the day. There is a 5/2 plan where you fast for two non-consecutive days of the week and eat normal on the rest of the days, five days of the week. And perhaps a alternate day fasting where you fast every other day and eat healthily in the in-between days.
There’s a lot of different formats here in terms of calorie restriction and time of eating, isn’t there?
So the 5/2 diet is perhaps appealing because there’s no calorie counting. This is our popular version of intermittent fasting where you eat a very low-calorie diet, around about 500 kilocals for two days of each week, and that’s any two days. And then the rest of the five days, you eat as normal. It is, of course, possible to lose weight with this diet, and it has been reported that it can improve several biomarkers of health, such as reducing levels of blood glucose and cholesterol. But really, the conclusions of the research is that it’s unlikely to be more effective for weight loss than traditional methods of dieting because it just actually reduces calorie intake to a similar extent as traditional dieting.
That would be dieting where you restrict calories for seven days of the week. So it’s a smaller restriction, but extended over different days. But of course, many people find it easier to follow the regime because it’s only two days of restriction and five days where you just eat healthily. So this intermittent calorie restriction equivalent is not superior to continuous calorie restriction but is just certainly another option. And we’re not really sufficiently– have sufficient information in order to understand who would benefit from what type of diet.
So time-restricted feeding is a particular type of intermittent fasting that compresses meals into a narrow time window for most people, and it usually involves skipping a meal, such as breakfast or dinner. And one of the common methods is the 18/6 diet where you fast for 18 hours and consume food only for six hours. One common finding is that people tend to reduce their food intake during the time-restricted feeding, even if they were not asked to. And of course, when you restrict calories, you may lose some weight, and that in itself can introduce health benefits.
A lot of the studies that have been published, I want to cite to the authors Longo and Panda, have done animal or murine-based studies where reported effects show improved glycemic control, decreased insulin, decreased postprandial glucose, that’s after eating, increased insulin sensitivity, and increased beta cell function, which is where the pancreas– where insulin’s released. So this would all point to really positive effects, and that would be during time-restricted feeding.
For example, could be only eating between 7:00 and 3:00 and then fasting for the rest of the day. The mechanisms are not clear, whether it’s you get improved medical health with no energy destruction, whether it’s due to altered peripheral circadian rhythm, whether the time of day of feeding and fasting is important, and the role indeed of the liver and glucose and lipid metabolism. So still a lot of unknowns with this regime.
So calorie restriction and longevity. So calorie restriction is associated with health improvements, increased longevity, and a reduction of morbidity or mortality, but that’s in animal studies. There’s less evidence of effect in humans. Calorie control also benefits our cardiovascular status, weight reduction, insulin sensitivity, diabetes control, cognitive function, and cancer prevention among its many effects in humans. But calorie restriction is difficult to practise and increases the risk of malnutrition. Intermittent fasting reduces the risk of malnutrition, and it’s easier to follow and is certainly gaining popularity. But more evidence for the benefit to humans is required.
So food for thought here as we finish off the lecture. Is body weight affected by how you eat? And this is an article that I published through The Conversation, which is looking at how changes in our circadian rhythm can impact on our physical and mental health. While there’s plenty of evidence supporting data and eating that’s more in line with our natural circadian rhythm, more research is needed to fully understand the effect that it has on body weight. We would say that most research studies show that intentional circadian rhythm disruption and night eating both cause what I call negative changes to many important hormones that regulate appetite, energy expenditure, and glucose regulation.
And that will result in changes in levels of different biomarkers circulating in the blood, such as insulin, leptin, cortisol, and other appetite hormones. Although it’s not known why this is the case, it might be because people who miss breakfast snack more in the evening, or it could be because later food intake disrupts the natural circadian rhythms. It should also be noted that not all studies agree that eating most of your day’s calories in the morning leads to a greater weight loss. So this is obviously a complex idea that we need more detail on. So hopefully you’ve enjoyed this short lecture and has given you a brief introduction to these learning outcomes.
As ever, if you’ve got any questions, please feel free–

Here is an interesting podcast from Professor Valter Lungo from the USC Leonard Davis School of Gerontology * Podcast from Prof. Valter Lungo on living to 110 years using fasting-mimicking diets

Here is an easy reading book on the topic by Dr Satchin Panda: The Circadian Code, 2018

This virtual issue brings together papers recently published in Nutrition Bulletin discussing different aspects of this fascinating area of research. To access the virtual issue click here: Chrono-nutrition – how important is when you eat?

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Nutrition Science: Lifestyle Medicine

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