23 studies on low-carb and low-fat diets part 2

After the first part of this article looked at the first 15 studies on the subject of low-carb vs. low-fat diets, this second part will take a look at the remaining 8 studies on the subject. This is followed by a summary and evaluation of the study results.

16 Shai I, et al. Weight loss with a low-carbohydrate, Mediterranean, or low-fat diet. New England Journal of Medicine, 2008.

Details: 322 obese subjects were randomly assigned to one of three groups following a low-carbohydrate diet, a reduced-calorie low-fat diet, or a reduced-calorie Mediterranean diet. The duration of the study was 2 years.

Weight loss: The low-carbohydrate group lost 4.7 kg, the low-fat group lost 2.9 kg and the group following the Mediterranean diet lost 4.4 kg.

Conclusion: The low-carbohydrate group lost more weight than the low-fat group and also showed greater improvements in HDL cholesterol levels and triglyceride levels.

17 Keogh JB, et al. Effects of weight loss from a very-low-carbohydrate diet on endothelial function and markers of cardiovascular disease risk in subjects with abdominal obesity. American Journal of Clinical Nutrition, 2008.

Details: 107 subjects with abdominal obesity were randomly assigned to a low-carbohydrate diet group or a low-fat diet group. The duration of the study was 8 weeks.

Weight loss: The low-carbohydrate group lost 7.9% of their body weight, while the low-fat group lost 6.5% of their body weight.

Conclusion: The low-carbohydrate group lost more weight. No differences in endothelial function or blood flow were observed between the groups, and no differences in common risk factors were observed between the groups.

18 Tay J, et al. Metabolic effects of weight loss on a very-low-carbohydrate diet compared with an isocaloric high-carbohydrate diet in abdominally obese subjects. Journal of The American College of Cardiology, 2008.

Details: 88 subjects with abdominal obesity were randomly assigned to a very low-carbohydrate diet group or a low-fat diet group. The duration of the study was 24 weeks. Both diets were calorie-restricted.

Weight loss: The low-carbohydrate group lost an average of 11.9 kg, while the low-fat group lost 10.1 kg. However, the difference was not statistically significant.

Conclusion: The low-carbohydrate group lost more weight. Triglycerides, HDL cholesterol, C-reactive protein, insulin, insulin sensitivity and blood pressure improved in both groups. Total and LDL cholesterol improved only in the low-fat group.

19 Volek JS, et al. Carbohydrate restriction has a more favorable impact on the metabolic syndrome than a low fat diet. Lipids, 2009.

Details: 40 subjects with increased risk factors for cardiovascular disease were randomly assigned to a low-carbohydrate diet group or a low-fat diet group. The duration of the study was 12 weeks. Both diets were calorie-restricted.

Weight loss: The low-carbohydrate group lost 10.1 kg, while the low-fat group lost 5.2 kg.

Conclusion: The low-carbohydrate group lost almost twice as much weight as the low-fat group, even though both groups consumed the same amount of calories.

This study is particularly interesting because the calorie intake was the same in both groups and so-called "advanced" lipid markers were measured. Several things are worth mentioning:

• Triglyceride levels decreased by 107 mg/dL in the low-carb group, but only 36 mg/dL in the low-fat group.
• HDL cholesterol levels increased by 4 mg/dL in the low-carbohydrate group, while they decreased by 1 mg/dL in the low-fat group.
• Apolipoprotein B levels decreased by 11 points in the low-carbohydrate group, but only by 2 points in the low-fat group.
• LDL particle size increased in the low-carbohydrate group, while it remained the same in the low-fat group. In the low-carbohydrate group, LDL particle size partially shifted from small to large (good), while in the low-fat diet there was a partial shift from large to small (bad).

20 Brinkworth GD, et al. Long-term effects of a very-low-carbohydrate weight loss diet compared with an isocaloric low-fat diet after 12 months.American Journal of Clinical Nutrition, 2009.

Details: 118 subjects with abdominal obesity were randomly assigned to a low-carbohydrate diet group or a low-fat diet group. The duration of the study was 1 year. Both diets were calorie-restricted.

Weight loss: The low-carbohydrate group lost 14.5 kg, while the low-fat group lost 11.5 kg. However, the difference was not statistically significant.

Conclusion: A greater reduction in triglyceride levels and a greater increase in both HDL and LDL cholesterol levels was observed in the low-carbohydrate group than in the low-fat group.

21 Hernandez, et al. Lack of suppression of circulating free fatty acids and hypercholesterolemia during weight loss on a high-fat, low-carbohydrate diet. American Journal of Clinical Nutrition, 2010.

Details: 32 obese subjects were randomly assigned to a low-carbohydrate diet group or a low-calorie, low-fat diet group. The duration of the study was 6 weeks.

Weight loss: The low-carbohydrate group lost 6.2 kg, while the low-fat group lost 6.0 kg. The difference was not statistically significant.

Conclusion: The low-carbohydrate group showed a greater reduction in triglyceride levels (43.6 mg/dL) than the low-fat group (26.9 mg/dL). LDL and HDL cholesterol levels decreased only in the low-fat group.

22 Krebs NF, et al. Efficacy and safety of a high protein, low carbohydrate diet for weight loss in severely obese adolescents. Journal of Pediatrics, 2010.

Details: 46 subjects were randomly assigned to a low-carbohydrate diet group or a low-fat diet group. The duration of the study was 36 weeks. Both diets were calorie-restricted.

Weight loss: The low-carbohydrate group lost more weight and also showed a greater reduction in BMI than the low-fat group.

Conclusion: The low-carbohydrate group showed a greater reduction in BMI. Different biomarkers improved in both groups, with no significant differences between the groups.

23 Guldbrand, et al. In type 2 diabetes, randomization to advice to follow a low-carbohydrate diet transiently improves glycaemic control compared with advice to follow a low-fat diet producing a similar weight loss.Diabetologia, 2012.

Details: 61 subjects with type 2 diabetes were randomly assigned to a group that followed a low-carbohydrate diet or a group that followed a low-fat diet. The duration of the study was 2 years. Both diets were calorie-restricted.

Weight loss: The low-carbohydrate group lost 3.1 kg, while the low-fat group lost 3.6 kg. The difference was not statistically significant.

Conclusion: There was no significant difference in weight loss between the groups. A significant improvement in glycemic control was observed in the low-carbohydrate group after 6 months, but dietary adherence was poor and this effect disappeared after 24 months at the end of the study as subjects had increased their carbohydrate intake.

The analysis of the study results

In this section, after a detailed review of the individual studies, we will attempt to summarize and evaluate the results of these studies.

Weight loss

Here is a graph showing the difference in weight loss between the studies we looked at. 21 out of 23 studies included data on weight loss.

In the majority of studies, a statistically significant difference in weight loss was observed (always in favor of the low-carbohydrate diet). There are also numerous other factors that are worth mentioning:

• The low-carbohydrate groups often lost 2-3 times as much weight as the low-fat groups. In some cases there was no significant difference.
• In most cases, calorie intake was reduced in the low-fat group, while the low-carbohydrate groups could eat as much as they wanted.
• When calorie intake was restricted in both groups, the low-carbohydrate dieters continued to lose more weight, although the difference was not always statistically significant.
• There was only one study in which the low-fat group lost more weight, although the difference was small (0.5 kg) and not statistically significant.
• In several of the studies, weight loss was highest at the beginning of the study. Then the subjects began to gain weight again as they neglected their diet.
• When the scientists looked directly at abdominal fat (the unhealthy visceral fat), low-carbohydrate diets had a clear advantage.

Two of the main reasons that low-carb diets are so effective are the high protein content and the appetite-suppressing effects of this diet. This automatically leads to a reduction in calorie intake.

LDL cholesterol

Despite the concerns that many people express, low carbohydrate diets generally do not increase total cholesterol and LDL cholesterol levels.

Low-fat diets can lower total cholesterol and LDL cholesterol levels, but this effect is usually only temporary. After 6 to 12 months, the differences are no longer statistically significant.

There are also some anecdotal reports from physicians treating patients on low-carbohydrate diets that these diets can lead to increases in LDL cholesterol levels and some other advanced lipid markers in a small percentage of patients.

However, no such adverse effect was observed in any of the studies reviewed above. The few studies that looked at advanced lipid markers only showed improvements.

HDL cholesterol

One of the best ways to increase levels of the "good" HDL cholesterol is to eat more fat. For this reason, it is not surprising to see that low-carbohydrate diets (which are richer in fat) increase HDL cholesterol levels more than low-fat diets.

Higher HDL cholesterol levels correlate with better metabolic health and a lower risk of cardiovascular disease. Low HDL cholesterol levels, on the other hand, are one of the key symptoms of metabolic syndrome.

18 of the 23 studies reported changes in HDL cholesterol levels:

As can be seen, low-carbohydrate diets generally increase HDL cholesterol levels, whereas these hardly change and in some cases even decrease with low-fat diets.

Triglycerides

Triglyceride levels are an important risk factor for cardiovascular health and are another key symptom of metabolic syndrome.

The best way to lower triglyceride levels is to eat less carbohydrates - and especially less sugar.

19 of the 23 studies reviewed reported changes in blood triglyceride levels.

It is clear that both low-carbohydrate and low-fat diets lead to a reduction in triglyceride levels, but this effect was much stronger in the low-carbohydrate groups.

Blood sugar, insulin levels and type 2 diabetes

In non-diabetics, blood glucose and insulin levels improved with both low-carbohydrate and low-fat diets and the difference between the groups was usually small.

3 studies compared low-carbohydrate and low-fat diets in subjects with type 2 diabetes.

In only one of these studies was adherence to the dietary guidelines good and a sufficient reduction in carbohydrate intake was achieved. This led to numerous improvements and a drastic reduction in the HbA1c value, which is an important marker for blood glucose levels.

In this study, 90% of the subjects in the low-carbohydrate group managed to reduce or eliminate their diabetes medication. In the other two studies, the differences were small or non-existent, as adherence was poor and subjects ended up consuming about 30% of their calories in the form of carbohydrates.

Blood pressure

When blood pressure was measured, it tended to drop on both the low-carb and low-fat diets.

How many people stuck with it to the end?

A common problem with weight loss studies is that many people drop out of the diet and drop out of the study before the study is finished.

I did an analysis of the percentages of subjects who completed the study in each group. 19 out of 23 of the studies I looked at reported this:

The average percentage of subjects who persisted to the end of the study was as follows:

• Average for the low-carbohydrate groups: 79.51%
• Average for the low-fat groups: 77.72%

There were no major differences here, but it is also clear from these studies that it is no more difficult to stick to low-carbohydrate diets than it is to stick to other diets. The reason for this could be related to the fact that low-carb diets seem to reduce hunger and that participants are allowed to eat until they are full.

This is an important point as low-fat diets usually involve calorie restriction and require people to weigh their food and count calories. In addition, people usually lose more weight during low-carb diets, which may increase motivation to continue the diet.

Are there any unwanted side effects?

Despite the concerns expressed by many health experts in the past, none of the studies reported any serious side effects that could be attributed to any of the diets used.

All in all, low carbohydrate diets were well tolerated and had an excellent safety profile.

It's time to retire low-fat diets

It's important to keep in mind that all of the studies we looked at were randomized controlled trials - the gold standard of science. All of these studies were published in reputable, peer-reviewed medical journals.

These studies are scientific proof that low-carb diets are much more effective than the low-fat diets that are still recommended around the world.

It's time to retire this low-fat fad!

Source: https://www.healthline.com/nutrition/23-studies-on-low-carb-and-low-fat-diets#section9