Health & Wellbeing

Caloric restriction beats fasting diets for weight loss, new trial finds

Caloric restriction beats fast...
A trial found fasting subjects lost as much muscle mass as fat, whereas those eating a calorie controlled diet lost mostly fat
A trial found fasting subjects lost as much muscle mass as fat, whereas those eating a calorie controlled diet lost mostly fat
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A trial found fasting subjects lost as much muscle mass as fat, whereas those eating a calorie controlled diet lost mostly fat
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A trial found fasting subjects lost as much muscle mass as fat, whereas those eating a calorie controlled diet lost mostly fat

A trial led by researchers from the University of Bath is questioning the value of popular fasting diets, finding a simple calorie-controlled diet is more effective at reducing weight. The trial also found fasting can lead to greater losses of muscle mass.

Intermittent fasting is a popular dietary phenomenon that can take a wide variety of forms, from time-restricted feeding patterns (limiting food intake to a few hours each day) to alternate-day fasting (eating every other day, or fasting for a whole day once or twice a week). The science is far from settled on whether these kinds of eating patterns are beneficial for weight loss or even general metabolic health.

The few robust controlled trials testing these diets have delivered mixed results, often suggesting intermittent fasting is no more effective that a straightforward calorie-controlled diet. A 2019 trial testing alternate-day fasting found it was safe and at least as effective as caloric restriction, and a more recent time-restricted feeding trial reached similar conclusions.

This new trial set out to investigate whether fasting generates any specific weight loss or metabolic improvements compared to a consistently fed control group consuming the same overall caloric intake. A small cohort of lean, healthy volunteers was randomly separated into three groups: a control group tasked with eating a diet restricted to around 1,500 calories a day, an intervention group fasting every other day and eating around 3,000 calories on their feeding day, and a third group fasting every other day but eating two times the recommended daily caloric intake on their feeding day (around 4,000 calories).

Essentially, the interventions were geared to explore whether fasting without any caloric restrictions made a difference to ultimate weight loss. The findings revealed the third group, those fasting without reducing their overall caloric intake, did not show any significant weight loss after four weeks.

The other fasting group, consuming a similar caloric amount in totality to the dieting group, did register an average of 1.6 kg (3.5 lb) weight loss after four weeks. However, the simple caloric restriction group lost an average of 1.9 kg (4.1 lb) after four weeks. So, even though the restricted fasting group essentially consumed the same amount of calories as the control, they did not lose as much weight.

“Many people believe that diets based on fasting are especially effective for weight loss or that these diets have particular metabolic health benefits even if you don’t lose weight,” explains James Betts, lead researcher on the project. “But intermittent fasting is no magic bullet and the findings of our experiment suggest that there is nothing special about fasting when compared with more traditional, standard diets people might follow.”

Perhaps even more importantly, the researchers found about half of the weight loss seen in the restricted fasting group was due to lost muscle mass. This contrasts with almost all of the weight loss in the control group seen coming from reductions in body fat content.

It is hypothesized that the greater loss of muscle mass in the fasting cohort could be related to a reduction in overall physical activity observed on fasting days. The researchers note this behavioral change is largely subconscious, indicating fasting subjects may not even realize they are reducing their physical activity on fasting days.

“Most significantly, if you are following a fasting diet it is worth thinking about whether prolonged fasting periods is actually making it harder to maintain muscle mass and physical activity levels, which are known to be very important factors for long-term health,” adds Betts.

Of course, as with all of these kinds of studies, there are limitations in how broadly the results can be interpreted. The trial was conducted in lean and healthy subjects, for example, so it is unclear whether fasting obese subjects would register greater fat reductions compared to the muscle mass loss seen in this study.

The researchers also note alternate-day fasting still may be a preferable intervention for some as it has been considered an easier dietary pattern to follow. It is advised that countermeasures to protect lean muscle mass, such as resistance training, are adopted if one chooses to follow alternate-day fasting protocols.

The new study was published in the journal Science Translational Medicine.

Source: University of Bath

11 comments
11 comments
Mike_S
Great study. I hope someone will add an intermittent fasting to this one, to check. I am not sure if the men's testosterone level raise after fasting is a fact or myth, but if it is true, then this one may help to maintain muscle mass (or even gain when supported with training). It is proven that amount of food one's eat next day after day of fasting is NOT 200% of normal intake. It is about 110 - 120%. And of course human psychology: maintaining caloric restriction is much harder than maintaing every other day fasting or day-to-day intermittent fasting.
McDesign
Yabbut - it's far easier to just restrict one's eating to a few hour window in the day, and worry less about WHAT you eat, than eating throughout the day and watching EVERYTHING you eat. Fasting isn't "better" it's just subjectively "easier" - and the best diet is the one you stick with.
Bob Flint
Calories in, needs to equal or be less than calories spent, will reduce the mass. Even simply lying still, or sitting at a screen.
WB1200
They need to test 16/8 intermittent fasting as Mike_S stated.
For what it's worth - I started intermittent fasting, 16hr fasting & 8hr feeding - keeping calories the same. In about 6 months I lost about 5 LBS. Doesn't sound like much but I wasn't "over weight" just want to get leaner. I'm 5'6" - went from 156LBS to 150LBS eating the same calories. I continue to do 16/8 but started doing Keto - in 3 months went from 13% to 8% body fat. Keto & 16/8 is a powerful combo at least for me:-) Oh, I'm a 53yo male so there's that:-P
LarryStevens
Wonder whether compliance varied across the groups. My expectation is that compliance was better on the fasting group than others.
Rusty Harris
My doctor wanted me to start checking my blood sugar...pre-diabetic. I've pretty much sworn off sugar, bread, pototo chips and what not.
I also started at the first of the year, delaying eating breakfast until 9am, and lunch until 1:30 PM. By the time I go home I am not hungry
and snack on no/low salt mixed nuts and sugar free lemonade.
I've tightened my belt almost 3 notches and dropped about 15 pounds in the process.
Jeff7
Agree with most of the comments - the different fasting ‘diets’ are much easier to stick with (and you choose whichever variant you prefer). If calorific control was so easy and effective everyone that had ever started a ‘diet’ would have successfully lost weight and kept it off - didn’t happen. With normal diets you’re hungry and missing chocolate every day of your life. Me - 5:2 works well. I’m only hungry for 2 (awake) days a week.
michael_dowling
I have lost ~ 12 lbs on a 14/10 intermittent fasting regime,which I started last November. In practice,I usually extend the fasting period by about 2 hours,as I am not hungry in the morning. So if I stop eating at 7pm,I commonly start eating again at 11am. Coffee is allowed, with up to half a cup of milk,as that contains 50 calories,which if not exceeded keeps the body in fasting mode. When I start eating,I eat anything I want,in whatever quantity i want. I tried caloric restriction dieting,but that is a miserable way of reducing weight,as you are always hungry.
Sean Ross
These studies can miss the point entirely. I have been doing 16hr for over 15yrs, last yr 18hr as it's gaining momentum as the sweet spot. I am 48 and put on muscle mass like a 25yr old, I gym with abundance of energy, I have high hgh and test, I am 12% b-fat, my bloodwork is impeccable as well. I take no supps other than vitd and some pure grassfed whey protein. I eat clean and whatever and however much I want. Most do not fast for weight issues, they fast for the improvement in all health markers, for autophagy, longevity, for a page full of biological benefits that occur when you enter a fasted state. These benefits do not occur from just 'watching calories', unless you go extreme caloric restriction. In closing, do not be under any illusion these two types of dieting (counting calories and fasting) are biologically remotely close.
Excalibur2811
I do intermittent fasting and find it effective and easy to stick to.. as others have said I do sometimes start my day with a coffee but thereafter eat nothing until about 2pm. When I tried dieting it simply became too frustrating to measure calories and more often than not I would just end up over-eating. The beauty with intermittent fasting is that the measurement of calories is simple.. until you eat you have consumed 0 calories. That is already inspiring in itself. The secret however is to include some exercise. At this time I am walking about 2.5Km daily and have a set daily step target of 6,500 steps. Having a smart watch helps a lot to keep me on track and I would recommend it to anyone trying to lose weight or stay healthy.