A Penn State study linked reduced calorie intake to longer, healthier lifespans. Photo / Getty Images
We all know it’s generally a good idea to eat less, but a recent scientific study has shown that cutting your calorie intake by 25% could help you live longer.
For women, that will mean cutting their calories by around 500 a day, from the recommended 2000 a day. Men will need to cut 625 calories from the usual 2500.
Researchers at the Penn State College of Health and Human Development have shown that calorie restriction effectively makes our cells “younger”.
A hundred and seventy-five participants were followed for two years to assess whether reducing calories by 25% lengthened their telomeres. Telomeres are the protective “caps” at the ends of chromosomes, the length of which indicates the rate at which cells are ageing.
The study found that those following the calorie restricted diet developed longer telomeres over the two years, making them biologically “younger”.
If reducing your calorie intake by 25% sounds like a tall order, evidence from earlier research into longevity, known as the Calerie study, also found that even a smaller 12% improved blood pressure, insulin sensitivity and inflammation markers.
This would mean a daily calorie reduction of 240 calories for women and 300 for men.
So how might we cut our calorie intake for similar benefits?
If you follow a low-calorie diet most days of the week, then splurge on one day that is effectively “calorie cycling”. Some dieters do this on purpose, to keep their metabolism on its toes. The theory being that a continuously restricted diet can lead to diminishing returns as our body adapts, while mixing up your diet with high- or low-calorie days can help keep your metabolism firing on all cylinders.
There’s no set pattern to calorie cycling so you can experiment to find a routine that works for you. Some people prefer to have five lower-calorie days and two higher-calorie days per week, others may find following a lower-calorie diet for two to four weeks before adding longer five- to seven-day higher-calorie periods is easier.
We tend to overeat by sheer force of habit, but most people can train themselves to eat less without noticing any difference in satiety levels. It’s thought our stomachs have an “appetite thermostat” and become accustomed to receiving a certain amount of food: if we turn it down, we will feel satisfied with less.
The easiest way to achieve this is to serve yourself 20% less than you usually would at mealtimes.
You can easily save 280 calories on a roast dinner, for example. Just stick to the recommended two slices of roast beef, instead of three, and eat three roast potatoes instead of five.
Registered dietitian Laura Clark advises using a smaller plate as it helps the brain redefine what’s “enough”. After finishing your food, wait 15 minutes for the satiety hormone leptin to kick in before deciding if you’re still hungry. Most likely you won’t be and you’ll easily meet your calorie reduction target.
There are a number of different ways you can use fasting to cut calories. Time-restricted eating (TRE) simply means eating within a set timeframe, so you might choose to stop eating at 7pm, then not eat again until 8am, for a 13-hour fasting window.
One study from 2020 found that even a relatively short fasting period of 10 hours (from 8pm to 6am, say) led to weight loss, a healthier body composition, lower blood pressure and decreased levels of blood lipids. A more recent study found that after 12 hours of fasting, the body switches from glucose to fat metabolism and protein production improves, along with autophagy. The right timeframe is probably the one you can stick to.
If you’re not someone who can stomach ongoing restrictions, you might prefer the fasting-mimicking diet (FMD). This is where you “fast” for five days per month, limiting your calorie intake to 800 (the normal recommended daily intake in the UK is 2500 for a man and 2000 for a woman), but eat normally for the rest of the time.
If five days feels impossible, the late Dr Michael Mosley’s Fast 800 advocates calorie restriction on two days per week. The Fast 800 advocates a moderately low-carb approach based on the principles of the Mediterranean diet, divided into either two or three meals; whichever best suits your lifestyle.
Fasting is not suitable for everyone*.
If all these rules sound too onerous then try calorie shaving instead. It’s easy to slash 200-300 calories from your daily intake by making a few basic swaps and tweaks:
* If you are pregnant or breastfeeding, have any medical conditions, or have a history of eating disorders you should seek advice from your GP or other medical professional before making any significant changes to your diet.
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