The advice used to be – eat less fat and eat more carbs. That advice held fast for about 30 years.

The consequence (short version) is that many of us became overweight or obese? And the incidence of type 2 diabetes tripled in that time.

Indeed, obesity and type 2 diabetes have gone hand in hand, becoming twin epidemics.

Studies over the past decade have consistently shown that the increase in calories underpinning these epidemics were due almost entirely to increased carbohydrate consumption,

Now, a low-carb diet is not only accepted as good protection against type 2 diabetes, the evidence tells us that carbohydrate restriction should be the first and immediate step in diabetes management.

Low carbs and weight loss

If carbs, especially ‘bad’ carbs (of the ultra-refined persuasion) have been a driver of obesity, the obvious question is: Will cutting back on carbs, and replacing them with protein and fats, lead to weight loss?

Yes it will.

As a terrific 2018 randomised trial showed, low-carb diets cause people to burn more calories.

Even better, the findings suggest that low-carb diets can help people maintain weight loss, making obesity treatment more effective.

About the study

The study, known as the Framingham State Food Study, or (FS)2, tightly controlled what people ate by providing them with fully prepared food-service meals for a 20-week period.

One group was put on a high-carb diet, another was out on a low-carb diet.

Carbs provided to the groups “were of high quality, conforming to guidelines for minimising sugar and using whole rather than highly processed grains”.

The Boston Children’s Hospital researchers carefully tracked participants’ weight. They also measured insulin secretion, metabolic hormones and total energy expenditure (calories burned).

Over the 20 weeks, total energy expenditure was significantly greater on the low-carbohydrate diet versus the high-carbohydrate diet.

At the same average body weight, participants who consumed the low-carb diet burned about 250 kilocalories a day more than those on the high-carb diet.

The authors said that if the experimental conditions had persisted, the low-carb participants would have enjoyed a nine-kilogram weight loss after three years.

Read more about that trial here.

Not any old carbs will do

A new study led by Harvard TH Chan School of Public Health has shown how best a low-carb diet should be structured.

The winning formula for weight-loss maintenance is a “low-carbohydrate diets comprised mostly of plant-based proteins and fats with healthy carbohydrates such as whole grains”.

This diet was associated with slower long-term weight gain.

This was in comparison to carbohydrate diets comprised mostly of animal proteins and fats with unhealthy carbohydrates like refined starches.

Plant-based proteins include seeds, grains, nuts, beans and lentils. Healthy whole grains include brown rice, oats and buckwheat.

These all contain healthier carbs than you get from sugar, potatoes, white rice etc.

What the researcher says

“Our study goes beyond the simple question of, ‘To carb or not to carb?’” said lead author Binkai Liu, research assistant in the Department of Nutrition.

“It dissects the low-carbohydrate diet and provides a nuanced look at how the composition of these diets can affect health over years, not just weeks or months.”

The study analysed the diets and weights of 123,332 healthy adults from as early as 1986 to as recently as 2018.

Each participant provided self-reports of their diets and weights every four years.

The participants were offered five categories of low-carbohydrate diet to sample or adhere to:

1. Total low-carbohydrate diet (TLCD), emphasising overall lower carbohydrate intake
2. Animal-based low-carbohydrate diet (ALCD), emphasising animal-based proteins and fats
3. Vegetable-based low-carbohydrate diet  (VLCD), emphasising plant-based proteins and fats
4. Healthy low-carbohydrate diet (HLCD), emphasising plant-based proteins, healthy fats, and fewer refined carbohydrates
5. And unhealthy low-carbohydrate diet (ULCD, emphasising animal-based proteins, unhealthy fats, and carbohydrates coming from unhealthy sources such as processed breads and cereals.

The study found that diets comprised of plant-based proteins and fats and healthy carbohydrates were significantly associated with slower long-term weight gain.

Participants who adhered more to diets 1, 2 and 5 on average gained more weight. That was compared to those who increased their adherence to diet 4 over time.

These associations were most pronounced among participants who were younger (less than 55), overweight or obese, and/or less physically active.

The results for the vegetable-based low carbohydrate diet were more mixed.

The senior author says

Qi Sun is senior author and associate professor in the Department of Nutrition.

He said: “The key takeaway here is that not all low-carbohydrate diets are created equal when it comes to managing weight in the long term.”

He said the findings could shake up the way we think about popular low-carbohydrate diets.

He said the public health initiatives should continue to encourage healthful foods like whole grains, fruits, vegetables, and low-fat dairy products.

It’s what we’ve been told many times before.