Low Carb? Low fat? What recent dietary studies tell us

Bacon and black coffee for breakfast, or oatmeal and bananas?

If you plan to lose weight in 2019, you will undoubtedly have a heated debate online and with friends and family about how you can best do this. It seems like everyone has an opinion and new fads appear every year.

Two major studies last year provided more fuel for a particularly polarizing issue – the role that carbohydrates play in making us fat. The studies gave scientists some clues, but like other food studies they can not say which diet – if any – is best for everyone.

That will not satisfy people who want black-and-white answers, but nutritional research is extremely difficult and even the most respected studies have big comments. People are so different that it is virtually impossible to conduct research that shows what really works during long periods.

Before we start a slimming plan for the new year, here is an overview of what we have learned last year.

Less carbohydrates, less pounds?

It is no longer called the Atkins diet, but the carbohydrate-rich school for diets has had a comeback. The idea is that the refined carbohydrates in foods such as white bread are quickly converted to sugar in our body, leading to energy fluctuations and hunger.

By cutting carbohydrates, the claim is that weight loss will be easier because your body will burn fat instead to use fuel while you are less hungry. A recent study seems to offer more support to supporters of low-carb. But, like many studies, it only tried to understand a piece of how the body works.

The study, led by an author of books promoting low-carbohydrate diets, investigated whether different carbohydrate levels could affect how the body uses energy. Among 164 participants, it found those on low-carb diets burn more total calories than those on high-carb diets.

The study did not say that people lost more weight to a low-carbohydrate diet – and did not try to measure that. Meals and snacks were tightly controlled and constantly adjusted so that everyone's weights remained stable.

David Ludwig, a lead author of the paper and researcher at Boston Children's Hospital, said it suggests that limiting carbohydrates could make it easier for people to lose weight if they lose it. He said the approach would work best for people with diabetes or pre-diabetes.

Ludwig noted that the study was not intended to test health effects in the long term or realistic scenarios in which people make their own food. The findings also need to be replicated in order to be validated, he said.

Caroline Apovian of the School of Medicine at Boston University said that the findings are interesting feeds for the scientific community, but that they should not be used as advice for the average person who wants to lose weight.

Do I avoid fat being thin?

For years, people were advised to rein in fats found in foods including meat, nuts, eggs, butter and oil. Cutting fat was seen as a way to keep the weight under control, because a gram of fat contains twice as many calories than the same amount of carbohydrates or proteins.

Many say that the advice had the opposite effect by giving us unintentional licenses to clean fat-free cookies, cakes and other foods that were instead full of the refined carbohydrates and sugars that are now responsible for our wider waists.

Nutritionists gradually moved away from general recommendations to limit fat for weight loss. Fats are necessary for absorbing important nutrients and can help us feel full. That does not mean you have to stay on steak drizzled in butter to be healthy.

Bruce Y. Lee, a professor of international health at Johns Hopkins, said that the lessons learned from the anti-fat craze should be applied to the anti-carb craze: not to simplify advice.

"There is a constant search for an easy way out," Lee said.

What is better?

Another big study of the past year was that low-carbohydrate diets and low-fat diets were about as effective for weight loss. The results varied per individual, but after one year people in both groups continued to spend 12 to 13 kilos on average.

The author noted that the findings do not contradict Ludwig's low-carb study. Instead, they suggest that there may be some flexibility in the ways we can lose weight. Participants in both groups were encouraged to focus on minimally processed foods such as products and meat prepared at home. Everyone was advised to limit added sugar and refined flour.

"If you have that basis right, for many, that would be a huge change," said Christopher Gardner of Stanford University and one of the authors of the research.

Limiting processed foods could improve most diets by reducing total calories while leaving room for people's preferences. That is important, because in order for a diet to be effective, a person must be able to hold on to it. A breakfast with fruit and oatmeal can be filled for one person, but leaves another hungry short thereafter.

Gardner notes that the study also had its limitations. The diets of participants were not checked. Instead, people were given instructions on how to achieve a low-carbohydrate or low-fat diet in regular meetings with dieticians, who may have provided a support network that most people do not have.

What works?

In the short term you can probably lose weight by eating only raw food, eating vegan food, removing gluten or following a different diet plan that you keep an eye on. But what will work for you in the long term is another question.

Zhaoping Li, director of clinical nutrition department at the University of California, Los Angeles, says there is no set of guidelines that helps everyone lose weight and keep them off. It is therefore why diets often fail – they are not responsible for the many factors that drive us to eat what we do.

To help people lose weight, Li examines the eating and exercise routines of her patients to identify improvements that people can live with.

"Which sticks is what counts," Li said.

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