New study: Lower-calorie keto diet works for overweight women

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Once again, a keto diet has been credited with helping people lose weight and improve their health.

In a new study from Polish researchers published last month, overweight and obese women who followed a calorie-restricted ketogenic diet experienced dramatic weight loss and improvement in several health markers:

Nature 2020: The effects of a low calorie ketogenic diet on glycaemic control variables in hyperinsulinemic overweight/obese females

In this randomized controlled trial, 100 women with chronically high insulin levels were assigned to follow either a keto diet containing 20% fewer calories than their calculated needs or to continue eating their usual diet for 12 weeks.

By the end of the study, women in the keto group had lost 30 pounds (13.6 kilos), on average. In an equally impressive change, their waist size decreased by an average of 4.5 inches (11.6 cm).

Additionally, their average fasting insulin levels and insulin resistance scores dropped by more than 50% and their fasting blood sugar levels dropped by 20%. Furthermore, the women’s triglycerides decreased from 213 mg/dL to 129 mg/dL and their HDL cholesterol increased from 37 mg/dL to 53 mg/dL, on average.

After just 12 weeks of keto eating, many of the women’s health markers — including fasting insulin — had improved so much that they were considered within the normal range.

The women in the control group didn’t experience any weight loss or beneficial changes in health markers. This isn’t surprising, given that they made no changes at all to their diet.

We do need to point out that the researchers chose to restrict both calories and carbs in the keto group.

Ideally, both groups would have either been calorically restricted or allowed to eat as much as they needed to feel full. Had that been done, it would have been easier to determine whether any beneficial changes were due solely to keto eating, rather than having to consider whether deliberate calorie restriction may have also played a role.

On the other hand, this wasn’t a very-low-calorie diet (800 or fewer calories per day), which has been used in many studies.

Women in the keto group reported eating roughly 1,800 calories daily, for an average deficit of about 450 calories per day. This deficit was calculated by subtracting each woman’s estimated energy expenditure (calories out) from the amount of calories they reported consuming (calories in).

Normally, a calorie deficit of this size would be expected to produce a loss of about 10 to 15 pounds within 12 weeks. The women in this study lost an average of 30 pounds in that time period!

Importantly, keto diets typically prompt the body to release a large amount of water initially, which likely contributed to some of the women’s overall weight loss.

However, even though changes in body composition weren’t reported, the decrease in waist size shows that much of the weight they lost over 12 weeks was likely fat. Since they reported adequate protein intake (about 90 grams per day, on average), we would expect lean body mass to remain stable or increase, although it would have been nice to objectively measure this.

Additionally, their dramatic improvements in insulin levels and other health markers are consistent with results from previous ketogenic diet research in which people were allowed to eat to satiety.

Yes, the keto group was mildly calorie restricted, but 1,800 calories per day is usually enough for most women to feel satisfied — particularly when eating nourishing, filling keto foods.

Indeed, the study authors noted:

After the experiment was completed, most of the women declared that they would continue this diet, not only for health reasons but because it is very practical in everyday life.

At Diet Doctor, we hope that most of these women do continue to eat low carb for the rest of their lives — and that many others who could benefit will choose to join them.

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