The answer, in both cases, was no.
But get this: It actually might not matter which one you go for. "Maybe we shouldn't be asking what's the best diet, but what's the best diet for whom?" But researchers were unable to find any link between dietary approach and superior weight loss.
However, because participants in the study did not strictly adhere to their diets (most simply ate whole, "real" foods instead of calculating the exact proportions of fat or carbs they consumed) Lustig notes that it's hard to explicitly claim that genetics weren't a factor in the weight loss.
The research lends strong support to the notion that diet quality, not quantity, is what helps people lose and manage their weight most easily in the long run. About half were men and half were women. HDL cholesterol or good cholesterol was raised in the HLC diet group only.
"Some previous studies that have damned carbohydrates have not taken note of the foods that supplied it".
"The finding of no significant difference in weight loss in genotype-matched vs mismatched groups in the current study highlights the importance of conducting large, appropriately powered trials such as DIETFITS for validating early exploratory analyses", reported the authors.
They also drank a shot of glucose on an empty stomach so researchers could measure their bodies' insulin outputs.
Of course, many dieters regain what they lose, and this study can not establish whether participants will be able to sustain their new habits.
"This is the key point not just for a weight loss diet but for a healthy diet to follow for life". The people in the low-carb group were actually eating relatively high amounts of carbs -they were nowhere near the next-to-nothing carb counts that people on regimens like the keto diet achieve.
Accused of misconduct, state Sen. Tony Mendoza suddenly resigns
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The strategy worked for people whether they followed diets that were mostly low in fat or mostly low in carbohydrates.
Weight loss averaged about 13 pounds over a year regardless of genes, insulin and diet type.
Some individuals lost far more - up to 27kg (60 pounds), while some gained 9kg (20 pounds). The findings were published in the Journal of the American Medical Association on February 20.
"This study closes the door on some questions - but it opens the door to others".
High-profile nutritionist Dr Rosemary Stanton said this was an "excellent" study.
And Professor Lennert Veerman from the School of Medicine at Griffith University said that the results suggests that "there is probably not such a thing as a diet that is right for your particular genetic make-up".
Gardner and his colleagues designed the study to compare how overweight and obese people would fare on low-carbohydrate and low-fat diets. "We told them all that we wanted them to minimize added sugar and refined grains and eat more vegetables and whole foods". Go for whole foods, whether that is a wheatberry salad or grass-fed beef. "But for that to work, most people will need an environment that encourages healthy eating, rather than one that is full of heavily advertised, convenient and affordable junk food". "And months into the study they said, 'Thank you!"
"I'm hoping that we can come up with signatures of sorts", he said.