The battle between low-carb and low-fat diets has been going on for longer than anyone can remember.

Dieters are often forced to pick a side and are left to do some serious head scratching when they need to decide which one of these diets to incorporate into their lives.

Despite numerous research studies, a clear conclusion over which one’s more effective for weight loss has never been drawn – and both diets have amassed plenty of supporters and opposers over time. In other words – some believed that the key to successfully shedding weight is giving up grains and fruits – while others would shake their heads and point at red meat, dairy and fatty foods.

Who’s the winner, then? Well, it turns out there isn’t one!

A major research study has found that neither low-fat nor low-carb diet is superior – and both are just as effective in aiding weight loss.

How did the study manage to evaluate their effectiveness, what did the research project involve – and what other success factors did the study uncover?

Let’s take a look at the study in a little more detail – and find the answers to these questions!

What Did The Study Involve?

The study was a year-long randomized clinical trial – a method which is usually used to determine which one of the two strategies (or in this case – diets) works best.

Carried out by Stanford University School of Medicine in the US, it managed to overcome the challenges that are often posed by research into diet effectiveness:

  • Recruiting a sufficient number of participants;
  • Tracking them over an extended period of time;
  • Carefully monitoring how well the participants are complying with the assigned diet.

Researchers at the university recruited over 600 adults aged 18 to 50 with an average BMI of 33 (considered to be class 1 obesity).

Before being randomly assigned to either a low-fat or low-carb diet, the participants underwent many different tests and measurements, such as their weight, insulin response to glucose, as well as tests for genetic factors linked to diet response.

Following these tests, researchers assigned them to one of the two diets.

Finding a Sustainable Level of Consumption

Participants in each group were instructed to follow a specific diet for the first two months: those on the low-carb diet were asked to consume not more than 20 grams of carbohydrates a day, while the low-fat diet group were instructed to consume only 20 grams of fat daily.

After eight weeks, participants in the low-carb group were instructed to add more carbs into their diet – until they felt that the diet would be sustainable at that level. The same was asked of the low-fat group.

It’s important to note that participants were never told to consume a certain amount of calories a day. They were instructed to:

  • Maximize vegetable intake;
  • Reduce/ minimize their consumption of refined flours, added sugars – and trans fats;
  • Eat foods that had a minimal level of processing, were rich in nutrients – as well as home-cooked whenever possible.

Researchers found that, by the end of the third month, the low-fat group had doubled their fat consumption to an average of about 42 grams daily. The low-carbs group, however, increased their intake of carbs to 96 grams per day.

What Did They Investigate Specifically?

To understand the factors that might influence an individual’s ability to gain/ lose weight, the study looked at the following:

  • Participants’ genomes. The researchers analyzed the participants’ gene patterns that could be associated with the effectiveness of carb or fat metabolism.
  • Participants’ insulin levels. Insulin levels have previously been linked to weight gain – therefore all subjects’ insulin levels were measured as part of the study.
  • Other outcomes, such as changes in body composition, blood pressure, cholesterol levels, fasting glucose/ insulin levels, resting and total energy expenditure.

What Did The Results Show?

The results showed no significant weight-loss differences between the two groups.

After 12 months of following the diet, the low-carb group lost 13.2 lbs (6kg), while the low-fat group lost 11.7 lbs (5.3 kg). These differences weren’t statistically significant.

Despite the difference in carb/ fat consumption levels, results revealed that it didn’t matter whether people focused on fat or carb intake. During the study, both groups consumed about the same number of calories on average each day – and even though there were some weight loss fluctuations between individuals, both groups managed to lose a similar amount of weight.

Participants in both groups also showed similar positive results in the following areas:

  • Body-fat percentage
  • BMI numbers
  • Waistline measurements
  • Blood pressure
  • Blood glucose levels
  • Fasting insulin

Researchers also found that differences in insulin secretion or genotypes did not make any significant difference in weight loss.

What Can We Take Away From This Low-Fat vs. Low-Carb Diet Study?  

To put it in simple terms, researchers involved in the study believe that the key to achieving successful weight loss results was instructing participants to focus on specific dietary behaviors and goals, rather than their calorie intake.

The participants were never instructed to “eat this much of that – and not that.” They were given the freedom to determine the lowest intake of either carbs of fat needed not to feel hungry – and, most importantly, to prioritize foods that were healthy and nutrient-rich.

This suggests that neither carb nor fat are more effective in aiding weight loss and that making sure that your diet program is designed to suit your personal preferences – and what you can sustain long-term – is crucial. 

Were There Any Noteworthy Differences Between the Two Groups? 

Even though the results were very similar, there were some interesting differences worth mentioning.

Those who followed a low-fat diet showed lower levels of LDL cholesterol (i.e., “bad” cholesterol).

However, while the level of “bad” cholesterol rose in the group that followed a low-carb diet, the levels of “good” cholesterol also increased.

Conclusion

To sum up, it turns out that whether you go for low-fat or low-carb isn’t that important after all.

Both low-fat and low-carb diets can be equally effective in achieving weight loss – as long as there is no difference in daily calories consumed, or protein intake.

According to the researchers involved in the study, the key to achieving a desired level of weight loss is being able to tailor the approach so that you can create a sustainable diet, which can be followed long-term.

Beth Coats, RD LN
Beth Coats, RD LN
Staff Writer at DietProbe
Beth is a registered dietician with over 20 years experience in general nutrition.
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