Low-Carbohydrate, High-Fat Diets (LCHF): Their Role In Weight Loss 


What Are These Diets?

LCHF diets are a big hit in the fitness world and lots of people of following them in order to trim the excess pounds away. In some cases, people following LCHF diets have said they work so much better for weightloss over traditional weight loss diets (by traditional I simply mean no significant manipulation of any one macronutrient). 

However, other people simply hate them and argue that there is no need to manipulate any one macronutrient to extremes in order to lose fat. It’s unnecessary and makes weight loss an even harder task! Well, whatever people say about LCHF diets, I think it’s safe to say they are here to stay. So let’s take a closer look at LCHF and see what the science actually has to say about them.

•A few important questions to ask regarding LCHF diets:•

What are LCHF diets?

What are the effects of LCHF diets on weight loss over non LCHF diets?

What are the mechanisms of action of LCHF diets for their weight loss actions?

The Composition Of LCHF diets

Although the definitions might vary between sources, the general outline of a LCHF diet might look something like this (Noakes and Windt 2017):

Moderate carbohydrate diet: ~ 26-45% of daily calorie intake

LCHF diet: ~ <130g carbohydrate per day or ~ <26% of daily total energy intake

Very LCHF (ketogenic) diet: ~ 20-50g carbohydrate per day or ~ <10% of a 2000 daily calorie intake

Weight Loss Effects And LCHF Diets: The Science

•Study 1•

In a randomised, parallel group trial study by Bazzano et al (2014), 148 men and women without cardiovascular disease and diabetes, underwent either a low carbohydrate, high fat [LCHF (< 40g carbohydrates per day)] or low fat, high carbohydrate [LFHC ( <30% of daily energy intake from total fat)] diet over a period of 12 months. Weight data was collected at 0, 3, 6 and 12 months. 

Results: After 12 months, participants in the LCHF diet (in comparison to the LFHC diet group) exhibited greater decreases in weight, fat mass, increase in HDL and a reduction in triglyceride levels. 

Conclusion: The LCHF diet was more effective in causing weight loss in individuals and reducing cardiovascular risk factors. Those looking to undergo a weight loss plan could consider using a low carbohydrate approach. 


Bazzano et al (2014). Figure shows the changes in body weight, fat mass, HDL and triglycerides over a 12 month period in men and women without cardiovascular disease or diabetes with either a LCHF or LFHC diet. 


•Study 2•

In a study by Krebs et al (2010), 46 severely obese adolescent participants underwent either 36 weeks of a high protein, low carbohydrate [(HPLC) ~ 20g carbohydrate per day] or a low fat, high carbohydrate [(LFHC) fat at 30% of total daily calorie intake] diet. Weight changes were measured at 13, 24 and 36 weeks. 

Results: At 36 weeks, there were significant reductions in body mass index (BMI) by both the HPLC and LFHC groups. However, the reductions in BMI were greater for the HPLC diet group. Loss of lean body mass (muscle) was not spared in the HPLC group. There were no adverse effects observed in cardiac function, metabolic profiles or subjective complaints by either diet groups. 

Conclusion: The HPLC diet may be a safe alternative weight loss approach for those who are severely obese. 


Krebs et al (2010). Figure shows the changes in BMI of severely obese adolescents over a period of 36 weeks following either a LFHC or HPLC diet. 

•Study 3•

In a study by Shia et al (2008), 322 moderately obese participants underwent a 2-year trial, following either a low-fat (LF) calorie-restricted (~ 30% of total daily calories from fat), Mediterranean (M) calorie-restricted (moderate fat ~35% of total daily intake) or an low-carbohydrate (LC) non calorie-restricted diet (~ 20g of carbohydrates per day). Calorie restriction was 1800 calories per day for men, and 1500 calories per day for women. 

Results: At the end of the 2 year study, the mean weight loss for the LF group was 2.9kg, the mean weight loss for the M group was 4.4kg and the mean weight loss for the LC group was 4.7kg. Increase in HDL (high density lipoprotein) was greatest for the LC group. The LC diet group showed the greatest initial reductions in weight loss during the first 1-6 months of the study. The LC also showed the greatest increases in weight following the 6-24 months before the end of the study (as carbohydrates were gradually increased to a maximum of 120g per day from 20g). 

Conclusions: The M and LC type diets might be effective for weight loss in moderately obese people. Participants started to gain weight in the LC group once carbohydrates were re-introduced. Obviously this was due to the fact that increased carbohydrate ingestion also results in increases in energy intake, resulting in the weight re-gain. As Shia et al (2008) point out, this is no necessarily the fault of the LCHF diet itself, but simply due to the consequence of its discontinuation (as with all diet interventions). 



Shia et al (2008). Figure shows the mean changes in weight loss over a period of 2 years in those that followed a LF, M and LC diet. 

•Study 4• 

In a 1-year randomised clinical trial by Alhassan et al (2008), 311 obese/overweight women followed a series of popular weight loss diets (Atkins, Zone, Ornish and LEARN). Atkins (< 20g carbohydrates per day for induction, then < 50g carbohydrates per day maintenance, non-restricted energy intake). Zone (40% carbohydrates, 30% protein, 30% fat, energy intake restricted). Ornish (< 10% from fat, energy intake not restricted). LEARN (~ 55-60% carbohydrates, 10% saturated fat, energy intake restricted). 

Results: At the end of the 12 month study, the mean weight loss of the Atkins group was 4.7kg, with 1.6kg loss on the Zone diet, 2.2kg loss on the Ornish diet and 2.6kg weight loss on the LEARN diet. Again, there was a significant improvement in high density lipoproteins (HDL) in the Atkins group. 

Conclusions: Low carbohydrate diets might provide an effective means for weight loss in obese/overweight people. 


•Study On Diet Adherence (Alhassan et al)•

In a 1-year randomised clinical trial, Alhassan et al (2008) investigated the adherence to various popular weight loss diets Atkins, Zone and Ornish) in 181 obese/overweight women.  The dietary adherence of these participants was assessed as the difference between their respective assigned diet’s recommended macronutrient goals and their self reported intake. The adherence was then compared with weight changes over the 12 month period between the three different diets.  

Results: Adherence scores were found to be 0.42 (Atkins), 0.34 (Zone) and 0.38 (Ornish). With weight changes over the 12 months, 5.3kg (Atkins), 2.3kg (Zone) and 3.0kg (Ornish). 

Conclusions: Weight loss was greatest for those groups in which adherence to a diet was highest. So the adherence rates were greatest for Atkins, followed by the Ornish diet which also coincided with the greatest amounts of weight loss. Adherence to a diet might play a more important role in weight loss over time than the composition of the chosen weight loss diet itself. 

PubMed_Central__Figure_1__Int_J_Obes__Lond___2008_Jun__32_6___985–991__Published_online_2008_Feb_12__doi_ _10_1038_ijo_2008_8.jpg

Alhassan et al (2008). Figure shows the correlation between weight changes over 12 months and the level of adherence to a particular weight loss diet. Tertile 1 is most adherent, Tertile 2 is least adherent. Atkins and Ornish were most adherent and also corresponded with the greatest changes in weight over the 12 months.

Possible Mechanisms For Weight Loss On A LCHF Diet

Interestingly, one of the potential mechanisms for the greater extents of weight loss seen in participants on a LCHF diet might come from increased satiety. This increased satiety would allow people on these diets to consume less calories without feeling hungry. This lower energy intake would lead to greater weight loss over time. Noakes and Windt (2017) highlight a collection of studies which all show greater extents of weight loss in those who followed LCHF non-energy restricted diets (ab-libitum) compared with those who followed LFHC energy restricted diets. Even on an non-energy restricted diet, those who followed a LCHF diet, did not (on average) consume more calories than those on the energy-restricted LFHC diets. This suggested that LCHF diets might exert (in part) their weight loss effects through reducing satiety (although the mechanism of this is not clear). Although Noakes and Winds (2017) point out, these potential mechanisms might occur through the increased satiety effects of higher protein intakes typically characteristic of lower carbohydrate diets and reduced rebounds in hypoglycaemia (caused through high carbohydrate foods). 


Noakes and Windt (2017). Figure shows the mean weight losses between those that followed a LCHF diet (non-energy restricted) and those that followed a LFHC diet (energy-restricted). Since those lost more weight on a non-restricted LCHF die (and consumed less calories than those on a LFHC diet), this suggests that a potential mechanism for action of LCHF diets is through increasing satiety (reducing hunger) even when calories are dropped lower.  


A second potential mechanism for the weight loss effects of LCHF diets is likely to come through a ‘metabolic advantage’ (Noakes and Windt 2017). Specially, this is likely to arise from two different effects:

•Thermogenesis (Thermic Effect Of Food)•

In low carbohydrate diets, protein intake is usually increased in order to compensate for the lack of carbohydrates and so to provide you with the necessary energy to function and keep powering vital physiological processes. Since protein digestion is highly inefficient, the amount of energy required to break it down (in comparison to carbohydrates and fats) is much higher. That means that from your total daily calorie intake, some of that will be used to power protein digestion (this is measured by the amount of heat given out in the digestion reaction). For instance: say you take in 2000 calories per day, your ‘effective calories’ (those used by the body) for a high carbohydrate diet might be closer to 1900 calories. ~ 100 have been used in the digestion of carbohydrate and given out as heat. However, with a high protein diet, your effective calories might drop down to ~ 1800 calories. Since protein digestion is inefficient, it takes more energy (now ~ 200 calories – given out as heat) to break down the protein. 

•Greater Protein Turnover For Gluconeogensis•

Glucose is needed to power your central nervous system, brain and red blood cells. So, it’s pretty important that your body get’s enough glucose! Glucose usually comes from the breakdown of glycogen. However, in lower carbohydrate diets, these glycogen stores gradually become depleted, meaning that the production of glucose has to come from somewhere else. In this case, protein breakdown (gluconeogensis). However, gluconeogenesis requires a lot of energy to be able to produce the necessary components for glucose formation. As a result, more calories are likely to be utilised when a diet is higher in protein than one consisting of higher carbohydrates. Again, say your total energy intake for the day is 2000 calories. If 100 calories are needed to power gluconeogensis, then your ‘effective calories’ are 1900. 

So What Is The Verdict?

One thing is clear: LCHF diets cause weight loss. Studies show that LCHF diets might provide more superior weight loss than higher carbohydrate diets. However, the exact mechanisms of this are not clear. It’s likely however that such mechanisms might occur through a ‘metabolic advantage’ effect (but this still needs further work).

When it comes down to following a weight loss diet, the important question, I think, comes down to adherence. Will you be able to stick to a type of diet long enough to lose weight and to keep it off. While LCHF diets might provide superior weight loss results (at least in the short-term), the question is whether it’s realistic for most people to maintain these into the long-term. Some people do ok with low carbohydrates and might even function better! Other people however just tank: they reach a point in which low-carbohydrates stop them from functioning all together! This is not great encouragement if you are on a weight loss plan. 

While LCHF diets provide another avenue for weight loss, I don’t think they are the magic bullet a lot of diet gurus make them out to be. Yes, the body can function on low carbohydrates (ketone production – more about this in my next article!), but whether it’s truly a feasible long-term solution for weight loss, I don’t think so (but that is just my opinion). On paper, people might be able to function with ketones alone as the primary source of energy, but in reality (with work, activity, daily life, stress), is low carbohydrate really an optimal approach? Do our bodies just work better in this day and age with more carbohydrates in our system? Interesting questions to ask! A lot more work needs to be done to assess how well these diets work in the long-term.

Any questions, ask away!


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