Low-carb vs. low-fat: What is better for weight loss?

Low-carb vs. low-fat: What is better for weight loss?

With the colder autumn weather, many people feel relieved. The bikini season is over and finally, the moment has come when we can wrap ourselves in sweaters and hide excess kilos in jeans. However, disappointment can occur the moment you find out that the sweater is no longer so completely oversize, and the pants are also a bit tighter…

Regular summer barbecues accompanied with alcohol simply took their cost, that’s why it’s time to do something extra with your weight. But where to start?

First, you google how to lose weight fast. At that moment, countless diets jump at you, and you do not know which one to try first. That is why in today’s article, we will take a closer look at two of them, namely the low-carb and low-fat diet. Finally, we reveal which diet is the most effective.

What about receiving necessary macronutrients on a low-fat and low-carb diet?

1. Low-fat diet

This is an eating style in which you try to reduce your fat intake as much as possible. The maximum fat intake that low-fat surveys usually work with is up to 20% of total daily energy intake. However, there are also studies that work with the concept of low-fat even if the fat intake is up to 30% of the total energy intake. [1]

2. Low-carb diet

This style of eating follows a certain restriction of carbohydrate intake in our diet. This type of diet can be divided into three stages according to the radicality of carbohydrate restriction. [2]

  1. Ketogenic diet  with a very low carbohydrate content – the carbohydrate intake must either be in the range of 20-50 grams or make up less than 10% of a diet containing 2,000 kcal per day, regardless of whether you get into ketosis (a condition where the body gets most of its energy from fats, and not carbohydrates).
  2. Low carbohydrate content diet – the intake of carbohydrates in the diet must be less than 130 grams per day or must be less than 26% of the total daily intake.
  3. Moderate low-carb diet – carbohydrates make up 26-45% of total daily energy intake.
 How to lose weight on a low carb diet

Low-carb or Low-fat diet: Which is more effective for weight loss?

For example, a recent study by Dr. Gardner, which attempted to compare the effects of low-carb and low-fat diets on fat loss, addressed this as the “diet strife”. [3]

His work was an exception because he had been monitoring his respondents over the year, checked their compliance with the established intake of individual macronutrients, and also took into account the genotypes of participants (genetic equipment, which he assumed could affect the success of weight loss). In total, individuals were divided into 15 genotypes (5 low-fat, 9 low-carbohydrate, and 1 neutral).

A total of 609 people (263 men and 346 women) without health problems participated in the study. These were randomly assigned to groups that consumed a low-carbohydrate or low-fat diet. Individual participants were 18-50 years old and their BMI ranged from 28-40, ie somewhere between overweight and grade 2 obesity. [4]

The research team focused on:

  • weight change of the participants
  • relationship between diet type and genotype
  • the relationship between a particular diet and insulin secretion

What did the participants’ diet look like?

  • During the first month, the researchers tried to get to know the study participants better. During this period, individuals followed their normal regime. Until then, they consumed their usual food and exercised as they had been used to.
  • For the next two months, the low-fat group received 20 grams of fat per day (strict low-fat diet) and the low-carb group received 20 grams of carbohydrates per day (ketogenic diet).
  • After two months, participants were asked to increase their intake of fats and carbohydrates to a minimum that would be sustainable for them in the long run. The following month, the low-fat group consumed approximately 42 grams of fat per day, and the low-carb group consumed less than 97 grams of carbohydrates per day.
  • Study participants did not have a clearly defined caloric intake but were instructed to maximize vegetable intake, minimize added sugar, refined flour, and trans fats.
  • At the same time, participants were to focus on eating whole foods such as nuts, fruits, vegetables, seeds, legumes, etc., as they are rich in nutrients. They should also minimize industrially processed foods.
  • During the study, the researchers performed a total of 12 controls (so-called 24-hour dietary recall (24HR)), monitoring the participant’s intake in the last 24 hours, while asking about specific foods and beverages consumed.
  • Adherence to eating habits was confirmed by changes in fats (lipids) in the blood that are specific to a given eating style.
What to eat with a low-carb and low-fat diet
  • Participants underwent a glucose tolerance test during the study. This included measuring insulin concentration 30 minutes after consuming 75 g of glucose. In this way, the researchers tested how carbohydrate metabolism responds to diet. You can also find more information about how insulin works in our bodies in the article Insulin sensitivity – how to increase it and avoid insulin resistance.

In order to monitor the changes, the researchers performed regular measurements at the beginning, in the 3rd, 6th, and 12th month.

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What results did the annual monitoring provided?

Average macronutrient intake and final weight loss

Low-fat48 %29 %21 %5.3 kg
Low-carb30 %45 %23 %6 kg
  • The difference in lost kilograms between the groups was only 0.7 kg, which the researchers did not consider to be a statistically significant difference.
  • The assumption that participants in the genotype group, which was supposed to help them lose weight, would achieve better results was not confirmed either.
  • Insulin secretion did not have a significant effect on weight loss either.

Significant differences between diets are not shown in other studies as well

Similar results were obtained by Dr. Hu and his team, who also focused on the connection between the mentioned diets (low-carb, low-fat) and weight loss. The research also lasted for one year and involved 148 adults. [5] 

  • The low-carb group was supposed to eat less than 40 grams of carbohydrates a day.
  • With the low-fat group, fat content was to account for less than 30% of total daily intake and less than 7% of intake was to come from saturated fats.

And the results? The low-carb group lost an average of 2.2 kg and 1.1% of body fat during the year, in addition, the group’s muscle mass ratio increased by 1.3%. No changes in weight, body fat percentage, or muscle were measured in the low-fat diet group. Again, these differences were not considered statistically significant.

Can we lose more whilst on low-carb?

However, let’s look at studies that show statistically significant differences in weight loss between the low-carb and low-fat groups, in favor of greater loss on the low-carb diet.

We can first mention the research of Halyburton and her team. They examined the effectiveness of the two diets in a group of 93 obese people. [6]

  • The study lasted 8 weeks.
  • Participants were divided into diet groups (low-carb or low-fat), both groups had lower caloric intake than they were used to, specifically consumed the same 6000 KJ.
  • After eight weeks, the low-carb group lost 7.8 kg and the low-fat group lost 6.4 kg.
  • The research team considered the differences to be statistically significant.

There were also statistically significant differences in weight loss between the two diets with Daly and his team. He divided 102 people who had type 2 diabetes into two groups (again, low-carb and low-fat), and at the same time, he reduced the size of portions consumed[7]

  • The study lasted 3 months.
  • After three months, the low-carb group lost 3.55 kg and the low-fat group 0.92 kg.
  • The research team considered the differences to be statistically significant.
Results of a low-carb and low-fat diet

A key factor of the success of a low-carb diet

Some studies show significant differences between the low-fat and low-carb diets, while others are almost negligible. How can someone know! However, one possible explanation is offered to help us uncover the work of Foster and his team, who studied 63 adults for one year. [8]

  • Participants were again divided into low-carb and low-fat groups.
  • The study lasted one year, but control measurements were taken at 3, 6, and 12 months.
  • After 6 months, the low-carb group lost 7% of their body weight, the low-fat group 3% of their body weight.

However, it should be mentioned that the statistically significant differences between the groups were only after three and six months, not after a year.

Could the duration of the diet affect the results?

It makes no sense to say that dieting time is the only key factor influencing results. At first glance, however, it is clear from denser studies that statistically significant differences appeared only if the diet lasted a shorter time (up to half a year). There were no significant differences between groups in the one-year studies.

This short-term weight loss in a low-carb diet may be due to muscle glycogen depletion and increased water excretion. However, it is a matter of days, weeks at most. Then adaptations take place when glycogen begins to be formed from non-saccharide sources. [9]

Thus, people who start a low-carb diet can enjoy weight loss after only a few days, but this is largely due to a lower percentage of water in the body and depleted glycogen stores, not particularly because of the fat loss. This loss can be as much as 2-3 kg. When switching back to the standard carbohydrate intake, they then regain their weight back.

Don’t underestimate protein intake

Whether you opt for low-carb, low-fat, or any other diet, never forget to receive enough protein, which should most often be in the range of 1.4-2 g/kg per body weight. [10]

If you are trying to lose weight, it is desirable to stick to the previously recommended upper limit. The reason may be, for example, the high thermal effect of proteins. In the long run, however, it can also affect the success of low-carb or low-fat diets.

How does the thermic effect work?

The thermic effect is the energy that our body must expend during the digestion and metabolism of a given macronutrient.

  • TEF of carbohydrates: 5–10 %
  • TEF of fat: 0–3 %
  • TEF of protein: 15–30 %

You can also read more about how the thermic effect works in the article Negative calories – a myth or an ideal way to lose weight?

Now, on a sample intake of 2000 kcal for a person weighing 70 kg (let’s call him Joseph, for example), we will demonstrate, how big of a difference can the intake of carbohydrates and fats play with a constant protein intake during a year. 

For all macronutrients we will work with the average value of the thermic effect: protein 22.5%, carbohydrates 7.5%, fat 1.5%. In both cases, we will expect a protein intake of 1.8 g/kg BW.

1. Low-carb diet

In this case, Joseph divided macronutrients as follows: P 126 g (504 kcal), C 100 g (400 kcal), F 122 g (1 098 kcal).

In a year, Joseph will consume:

  • 45 990 g protein (183 960 kcal), burns 41 391 kcal during its thermic effect.
  • 36 500 g of carbohydrates (146 000 kcal) burns 10 950 kcal during its thermic effect.
  • 44 530 g of fat (400 770 kcal), burns 6 012 kcal during its thermic effect.

The total annual thermic effect whilst on a low-carb diet is in our case 58 353 kcal, which corresponds to the burning of approximately 7.6 kg of pure fat.

2. Low-fat diet

In this case, Joseph divided macronutrients as follows: P 126 g (504 kcal), C 300 g (1200 kcal), F 33 g (297 kcal).

In a year, Joseph will consume:

  • 45 990 g protein (183 960 kcal), burns 41 391 kcal during its thermic effect.
  • 109 500 g of carbohydrates (438 000 kcal), burns 32 850 kcal during its thermic effect.
  • 12 045 g of fat (108 405 kcal), burns 1626 kcal during its thermic effect.

The total annual thermic effect whilst on a low-fat diet is in this case 75 867 kcal, which corresponds to the burning of approximately 9.85 kg of pure fat.

From the above calculations, a difference in the thermic effect between a low-carb and a low-fat diet can be seen at first glance, in favor of a low-fat diet. However, the question remains to what extent these results would be influenced by other factors. Despite the fact that such low-fat intake can disrupt the hormonal conditions in both men and women. Therefore, a more sensible solution is to ensure a sufficient intake of protein, because these have the highest thermic effect, and eat a diet that will suit you in the long run.

If you don’t know how to supplement protein, you can help yourself for example with whey protein or get inspired by our article about protein sources.

Protein intake during weight loss

Which diet is the best for weight loss?

If we are to talk about the most effective diet, there is a universal answer to it. It is the one that you can maintain in the long run. When someone loves pastry, pasta, and rice, a low-carb diet is unlikely to be optimal for them. If you are attracted to low-carb because of the idea that you will lose weight fast, always keep in mind that the body first gets rid of water due to depleted muscle glycogen. If you have 2 kg less after three days on a low-carb diet, you have certainly not lost 2 kg of fat, but you have definitely lost 2 kg of water.

If you have decided that you want to lose a few pounds after the summer, we recommend that you start by setting a sufficient protein intake that can be up as the upper recommended limit (2 g/kg TH). At the same time, keep in mind that you will not deceive the income-expenditure equation. If you stick to a caloric deficit, it’s up to you how to play with carbohydrate and fat intake. However, always set their ratio so that weight loss is pleasant for you and you do not have to completely deny yourself all the foods you like. This is the only way you can achieve your dream goals.

Was this article useful for you and did it help you to explain the issues of low-carb and low-fat diets? If so, share it with your friends to help them achieve their goals.


[1] Priyanka Bhandari, Amit Sapra (2020) – Low Fat Diet – https://www.ncbi.nlm.nih.gov/books/NBK553097/

[2] Richard D.FeinmanPh.D. a kol. (2015) – Dietary carbohydrate restriction as the first approach in diabetes management: Critical review and evidence base – https://www.sciencedirect.com/science/article/pii/S0899900714003323?via%3Dihub#

[3] Christopher D Gardner a kol. (2018) – Effect of Low-Fat vs Low-Carbohydrate Diet on 12-Month Weight Loss in Overweight Adults and the Association With Genotype Pattern or Insulin Secretion: The DIETFITS Randomized Clinical Trial – https://pubmed.ncbi.nlm.nih.gov/29466592/

[4] Doleček, Středa, Cajthamlová (2013) – Nebezpečný svět kalorií – ISBN 978-80-249-2113-6

[5] Hu a kolektiv (2015) – Adherence to low-carbohydrate and low-fat diets in relation toweight loss and cardiovascular risk factors – https://onlinelibrary.wiley.com/doi/epdf/10.1002/osp4.23

[6] Halyburton a kol. (2007) – Low- and high-carbohydrate weight-loss diets have similar effects on mood but not cognitive performance – https://academic.oup.com/ajcn/article/86/3/580/4649430

[7] Daly a kolektiv (2005) – Short‐term effects of severe dietary carbohydrate‐restriction advice in Type 2 diabetes—a randomized controlled trial – https://onlinelibrary.wiley.com/doi/full/10.1111/j.1464-5491.2005.01760.x

[8] Foster a kolektiv (2003) – A Randomized Trial of a Low-Carbohydrate Diet for Obesity – https://www.nejm.org/doi/full/10.1056/NEJMoa022207

[9] Ebbeling a kolektiv (2007) – Effects of a Low-Glycemic Load vs Low-Fat Diet in Obese Young Adults – https://pubmed.ncbi.nlm.nih.gov/17507345/

[10] Jäger a kolektiv (2017) – Journal of the International Society of Sports Nutrition – doi:10.1186/s12970-017-0177-8

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