Low Fat Diet Vs Low Carbohydrate Diet? An Important Study Concludes: It Doesn’t Matter To Lose Weight

This study is notable for its large group of participants (more than 609 participants) of long duration (12 months) and careful dietary control.

A one-year randomized clinical trial found that a low-fat diet and a low-carbohydrate diet produced similar weight loss and improvements in metabolic health markers.

Furthermore, insulin production and the genes tested had no impact on the prediction of weight loss success or failure. Therefore, you should choose your diet based on personal preferences, health goals, and sustainability.

Previous studies comparing low-fat to low-carbohydrate diets have shown that individual weight loss can vary greatly within assigned diet groups.

The reasons for these individual responses are not well understood, leading scientists to hypothesize that perhaps insulin sensitivity or certain genetic components could explain the success or failure of different diets.

The current study evaluated whether differences in genetics or insulin production could help predict weight loss success in participants who followed a low-fat or low-carbohydrate diet for one year.

Who was studied?

This randomized clinical trial (RCT) assigned 609 participants to a low-fat or low-carbohydrate diet for 12 months.

In total, 263 men and 346 premenopausal women free of significant health conditions (ie, no diabetes, cancer, heart disease, high cholesterol, etc.) were included in the study. The mean BMI was 33 (class I obesity) and the mean age was 40 ± 7 years.

During the course of the study, each subject was instructed to attend 22 dietary counseling sessions with a registered dietitian; the average attendance was 66% for both groups.

During the first two months of the study, the low-fat group was instructed to consume only 20 g of fat per day and the low-carbohydrate group only 20 g of carbohydrates per day.

However, they were not expected to stay at these levels indefinitely: at the end of this 2-month period, they began adding fat or carbohydrates to their diet until they felt they had reached the lowest intake level that they could sustainably maintain.

Neither group was able to stick to the very low starting intakes: by month 3, the low-fat group was already consuming an average of 42 g of fat per day, while the low-carbohydrate group was consuming an average of 96.6 g of carbohydrates per day.

It is possible that some in the low carb group may have been in ketosis for these first two months due to the very low carb intake prescribed.

While the low-carb group was able to achieve a reduced carbohydrate intake during the trial (115 g / day), only a very small minority reported consuming ≤50 g / day, the intake threshold typically required to remain in ketosis. .

While no caloric intake targets were assigned, both groups were instructed to consume high-quality whole foods and beverages.

Specifically, they were instructed to “maximize the intake of vegetables, minimize the consumption of added sugars, refined flours, and trans fats; and focus on whole foods that were minimally processed, nutrient-dense, and prepared at home whenever possible. ”

A total of 12 unannounced, randomized multidirectional dietary withdrawals were taken during the study to assess food consumption.

Using this method, an interviewer asks people to recall all the foods and drinks they consumed in the last 24 hours. If you’re curious, you can try a 24-hour multi-pass withdrawal here.

Dietary compliance was also corroborated by changes in blood lipids and respiratory exchange ratio (RER: this may indicate whether you are primarily burning fat or carbohydrates).

What was studied?

The first primary hypothesis tested is a possible link between genotype pattern and diet type for weight loss success.

All participants were tested for 15 genotypes, including 5 ‘low-fat’ genotypes (hypothesized to perform better on a low-fat diet), 9 ‘low-carbohydrate’ genotypes (hypothesized to perform better on a low fat diet). low carbohydrate diet) and 1 “neutral” genotype.

The second main hypothesis being tested is a possible link between insulin secretion and type of diet for weight loss success.

At the start of the trial and at months 3, 6, and 12, all participants completed an oral glucose tolerance test (OGTT) to measure insulin production.

An OGTT is a test that can measure your blood glucose and / or insulin levels after you have consumed a fixed amount of carbohydrates (usually 75 g of glucose).

Other measured outcomes included changes in:

  • Body composition (assessed using DXA).
  • Cholesterol levels
  • Blood pressure.
  • Fasting glucose and insulin.
  • Energy expenditure at rest.
  • Total energy expenditure.

What was the results?

In total, 481 participants completed the full trial, which translates to a 21% dropout rate, which is not unexpected for a diet study of this length.

While there were no significant dietary differences between the groups at baseline (before dietary interventions began), there were significant differences at months 3, 6, and 12 with regard to percent intake of carbohydrates, fats, proteins, fiber, and added sugars. .

Furthermore, the intake of saturated fat was significantly reduced in the low-fat group, while the global glycemic index was lower in the low-carbohydrate group.

While both groups saw reductions in glycemic load, the decrease was much greater in the low-carb group.

The study showed no significant difference in weight loss between the low-fat and low-carb groups.

At 12 months, the low-fat group had lost 11.7 lbs (5.3 kg) and the low-carb group 13.2 lbs (6.0 kg); this difference of 1.5 lbs over 12 months (0.125 lbs / month) is not statistically significant or clinically relevant.

Furthermore, within each group, differences in genotypes or insulin secretion did not make a significant difference in weight change.

This suggests that neither the genotype tested in this study nor the amount of insulin produced during OGTT can predict weight loss success on a low-fat or low-carbohydrate diet.

Ironically, a possible confounder masking an interaction could have been that both diets were based on whole foods.

If, for example, the low-fat diet had consisted primarily of sodas and refined grains, the resulting insulin resistance might have had an effect on weight change.

Both groups were able to improve certain health markers (BMI, body fat percentage, waist circumference, blood pressure and fasting insulin and glucose levels), although no significant differences were observed between the groups.

At the 12-month mark, low-density lipoprotein cholesterol (LDL-C) had decreased significantly in the low-fat group (-2.12 mg / dL), while it had increased in the low-carbohydrate group (+ 3.62 mg / dL).

However, the low-carbohydrate group also experienced a significant increase in high-density lipoprotein cholesterol (HDL-C) (+2.64, versus +0.40 mg / dl in the low-fat group) and greater reductions in triglycerides (-28.20 vs -9.95 mg / dL in the low-fat group).

Resting energy expenditure (REE) was not significantly different between the groups at any point. By month 12, REE had decreased significantly since the start of the study for both groups (-66.45 kcal for low fat, 76.93 kcal for low carb).

Total energy expenditure (TEE) was not significantly different between groups or compared to baseline. Finally, although slightly more than 10% of each group improved their metabolic syndrome during the trial, there were no significant differences between the diets.

What does this study tell us?

The results of this study contribute to a large body of evidence indicating that, for weight loss, neither low fat nor low carbohydrate is superior (as long as there is no difference in caloric intake or protein intake).

In this trial, overall caloric intake was nearly identical between groups throughout the intervention period, with the low-carb group consuming only slightly more protein (an additional average of 12.5 g / day).

The weight loss results in this study are repeated in both short-term, strictly controlled clinical trials, and long-term, less controlled free-living clinical trials. While this study is a free-life test, it offers some advantages that are not seen in most of the others:

  1. The program offered intensive dietary counseling and guidance throughout the duration of the study. Many free life trials provide advance instruction and / or support, after which participants are left to their own devices.
  2. He confirmed the participants’ dietary intake through randomized dietary reminders from multiple 24-hour passes, reinforced by lipid panels and RER tests. Most long-term diet trials simply use 24-hour reminders or food frequency questionnaires.
  3. The study strongly encouraged its participants to eat healthy diets rich in whole foods and not fill their pantries with low-fat or low-carb junk food.

It is one of the largest studies of its kind, reducing the chances that a result is due to random error (also known as “noise”).

While our understanding of genetics-diet interactions continues to grow, this trial has tested 15 genotype patterns that are suspected of influencing the success or failure of weight loss on low-fat or low-carbohydrate diets.

While the measure of insulin production used in this trial could not predict weight changes, the authors note that based on other studies, fasting insulin measures may be worth further investigation as predictors of weight loss. .

Finally, not all participants adhered perfectly to the assigned diet, which reduces our ability to establish a direct relationship between genotype, insulin production, and dietary intervention.

However, the study results are still highly suggestive of a relationship, and the authors plan to do further analysis that takes into account dietary adherence.

What is to be considered from this?

An important aspect of this test that we must consider, and that is often overlooked, is the inter-individual variability.

Studies attempt to discern a global effect and often report nothing else, even when individual responses are all over the place.

A second important aspect to consider is adherence. At the beginning of the study, all participants were instructed to consume ≤20 g of fat (if they were in the low-fat group) or ≤20 g of carbohydrates (if they were in the low-carbohydrate group) for the first two months.

They could then increase their fat or carbohydrate intake to levels that they felt they could sustain indefinitely. At the end of the trial, the vast majority had not been able to maintain such low levels.

The final dietary recalls reported an average daily fat intake of 57 g (low-fat group) and an average daily carbohydrate intake of ≈132 g (low-carbohydrate group).

Real-life applicability matters a lot when extrapolating from study results. The results of this study send a clear message that when choosing an eating style, sustainability is a component whose importance cannot be underestimated.

There is no “best diet.” Low-fat, low-carb diets can work for weight loss; the healthy diet that will work for you is the one you can stick to.

The bottom line

  • When it comes to losing weight, neither a low-fat diet nor a low-carb diet is inherently superior.
  • Neither insulin production nor the genotypes tested had any notable effect on the success or failure of weight loss.
  • Choose an eating style that suits your food preferences, health goals, lifestyle. The most important thing is to choose an eating style that you can stick with.