The keto diet relies on eating minimal carbs while maintaining high fat consumption, which forces your body to fuel itself using compounds known as ketone bodies that come from stored fat.1
By comparison, the standard low fat diet comprises getting less than 30 percent of your total daily calories from fats, while more intensive versions comprise getting just 10 to 15 percent of your daily calories from fat. The idea here is that fat provides more calories per gram than proteins and carbs, which potentially means more calories stored as fat.2
However, if you are looking to lose weight, a low carb or keto diet may be more effective than a low fat diet. Read on to learn why.
Scientific Evidence: Low Carb vs. Low Fat
Numerous studies suggest the benefits of low carb diet over a low fat diet.
In a two-year trial, researchers randomly assigned 322 subjects with moderate obesity to three different diets: a Mediterranean diet with restricted calories, a low fat diet with restricted calories, or a low carbohydrate diet without any restricted calories. In the first year, the rate of adherence to each diet was 95.4 percent, while it was 84.6 percent in the second year.
The group assigned to the Mediterranean diet, which mainly comprises eating more plant-based foods and healthy fats, was found to consume the largest amount of dietary fiber among the three groups and had the highest ratio of monounsaturated fats to saturated fats.
The low carbohydrate diet group consumed the smallest amount of carbohydrates but the highest amount of fats, protein, and cholesterol and showed the highest percentage of ketones in subjects’ urine. Furthermore, the low carbohydrate group showed the highest average weight loss of 4.7 kg, while the Mediterranean diet group had an average weight loss of 4.4 kg. The low fat diet group had an average weight loss of just 2.9 kg.
Among the 272 subjects who finished the study, the mean weight loss was 5.5 kg for the low carbohydrate diet group, while the low fat group had a mean weight loss of 3.3 kg. The low carbohydrate group also showed a higher reduction in the ratio of total cholesterol to high-density lipoprotein (HDL) cholesterol at 20 percent, while the low fat group had a reduction of just 12 percent. This all suggests that the low carbohydrate diet may be a more effective alternative to the low fat diet for its more favorable effects on lipids (fat), cholesterol, and weight loss.3
Another study compared low fat and low carbohydrate diets directly. Researchers randomly assigned 132 subjects with severe obesity to either a fat-restricted or carbohydrate restricted diet. The subjects had a mean body mass index of 43 and a high prevalence of diabetes. Of these subjects, 79 completed the full six-month study.
Even taking into account those who dropped out of the study, researchers found that those assigned to the low carbohydrate diet lost more weight and had greater reductions in triglyceride levels compared to those on the low fat diet.
Researchers also measured insulin sensitivity in subjects without diabetes, and the results showed that the low carbohydrate group showed greater improvements in insulin sensitivity than subjects in the low fat group. This suggests that on top of greater weight loss, a low carbohydrate diet may improve insulin sensitivity and triglyceride levels, which means restricted carbs may also help heart health. However, further research is required to determine if a low carbohydrate diet could indeed support cardiovascular health.4
Triglycerides and Cholesterol
In a randomized controlled trial, researchers assigned 120 overweight subjects with hyperlipidemia to either:
- A low carbohydrate diet (less than 20 grams of carbohydrates per day) with nutritional supplementation, exercise recommendation, and group meetings
- A low fat diet (less than 300 mg of cholesterol per day, less than 30 percent of calories from fat, and deficits of 500 to 1,000 kcal per day) with exercise recommendation and group meetings
By the end of the 24-week study, more of the subjects in the low carbohydrate group than the low-fat group actually completed the study (76 percent and 57 percent, respectively).
At the end of the 24-week period, the low carbohydrate group showed greater overall weight loss and reductions in serum triglycerides along with increased high-density lipoprotein cholesterol (good cholesterol) levels.
This suggests that the low carbohydrate diet offers greater weight loss potential than low fat diets. While it’s not possible to draw relationships, it also should not be ignored that the participation retention was higher with the low carbohydrate group than the low fat group.5
How to Do a Low Carb Diet
The general low carb diet comprises high protein and low carbs with an emphasis on fruits, vegetables, meat, nuts and seeds, and healthy fats. At the same time, you will minimize high carbohydrate foods, including processed grains, starches, sugary drinks, and junk foods that are high in sugar and sodium.
If you want to learn how to do a low carb diet, you have several options ahead of you. The typical low carb or carb-restricted diet has no specific parameters and depends on your specific goals, preferences, and health needs. Common guidelines may comprise:
- 100 to 150 grams of carbohydrates per day to maintain current weight or for frequent high-intensity physical activity
- 50 to 100 grams of daily carbs for weight maintenance or steady weight loss
- Less than 50 grams of carbohydrates for “fast weight loss”
How to Do a Keto Diet
Keto diets rely on high protein, high fat, and extremely low carbs (usually less than 50 grams per day). This forces your body into a ketogenic state wherein your body releases fatty acids from its fat stores. These fatty acids go to your liver and changes them into ketones, which provide fuel for your brain and body. Keto benefits those looking to lose weight and control their appetite.6 Variations on the keto diet include:
- Cyclical ketogenic diet (CKD) – This diet maintains a regular ketogenic diet on most days but allows you to switch to a high-carb diet 1 to 2 days per week.
- Targeted ketogenic diet (TKD) – In this variation, you maintain your regular ketogenic diet but allow for higher carb intake around your workout days.
The low carb and keto diets remain a better option than a low-fat diet. Low carb and keto benefits include greater weight loss, decreased triglycerides, and improved cholesterol. However, carbohydrates are not bad or unhealthy in and of themselves.
Carbs are part of a balanced diet and, like any food, rely on moderation. Most importantly, avoid processed carbs, which are easily absorbed and turned into stored fat. For example, eating an apple is better than drinking apple juice. Apples provide dietary fiber, which keeps you full and supports your digestive health, and carbohydrates that are more slowly absorbed. On the other hand, apple juice is often high in sugar and sodium, which are absorb faster and easier, adding to your weight.
Weight loss is more often about food choices than cutting out any one macronutrient, but moderating your carbohydrate intake with a low carb or keto diet may be an ideal place to start.
Next article: Explaining the Keto Diet - Why the Food Pyramid is Wrong