Records exist of low carb diets being utilised as early as the 1800s, and since the 1970s, low carbohydrate diets have been increasingly used as a strategy for weight loss[1].
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The primary hypothesis of the effectiveness of low carbohydrate diets is referred to as the carbohydrate-insulin model.
This hypothesis posits that by lowering the amount of carbohydrates consumed, insulin (an anabolic, fat-storing hormone) secretion is reduced, leading to increased weight loss[1].
Additional factors that may contribute to the weight loss experienced include the following:
- Suppression of appetite-enhancing hormones e.g. ghrelin, and increased satiety
- Increased resting metabolic rate
- Higher overall energy expenditure
There are a number of low carbohydrate diets which promise to deliver reductions in body fat, higher energy levels and improved overall health.
The reduced carbohydrate intake of these diets has been associated with improved insulin sensitivity profiles and improved biomarkers for various diseases, including cancer and dementia[2].
Low carbohydrate food pyramid
Low carbohydrate diets share a similar overall structure, where the traditional food pyramid is reversed[3].
The majority of calories come from fats, followed by proteins and the small remainder coming from non-starchy carbohydrates[1].
Although the carbohydrate content of these diets is low, there is a lack of consensus on the exact level of carbohydrates that constitutes low carb.
Commonly followed variations of low carb include Classic Keto, Atkin’s diet and the Carnivore diet.
Although the overall structure is similar, there are a number of differences, some significant and others more nuanced[1].
Classical keto
Macronutrient split: 70% Fat | 20-25% Protein | 5-10% Carbohydrate
Overview
Classical keto is a high fat, moderate protein, low carbohydrate diet, that was initially used to treat epilepsy in 1921[2].
Since then, it has become increasingly popular as a method to lose body fat rapidly. During keto, very low amounts of carbohydrates (20-50g on a 2000kcal diet) are consumed in order to initiate ketosis.
Unlike other diets, the classical keto does not necessarily restrict calories. Instead, it focusses on maintaining a healthy caloric intake, but switching to fat as the primary source of body fuel[2][3].
Keto can produce exceptional weight loss results as well as a host of other health benefits[4]. However, due to the strict carbohydrate requirement, keto can be quite restrictive, meaning adhering to the diet is difficult for some people.
Side effects
Commonly reported side effects of keto, often referred to as the ‘Keto-flu,’ are associated with the initiation of the diet and normally resolve within a few days to weeks[2][4]. These include;
- Nausea and vomiting
- Headache
- Fatigue
- Dizziness
- Insomnia
- Reduced exercise tolerance
- Constipation
Although the short-medium term (up to 2 years) effects of keto are well studied, data is lacking on the longer term effects and potential drawbacks[2][4].
Atkin's diet
Macronutrient split: 65% Fat | 30% Protein | 5% Carbohydrate
Overview
The Atkin’s diet is a modified ketogenic diet, that again focuses on calories from fat, but with a higher protein content. Some refer to Atkin’s as the ‘original’ keto diet, and was popularised in the 1970s after the publication of Dr. Atkins’ Diet Revolution[5].
The cardiologist Dr. Robert Atkins developed the diet after becoming disillusioned with the use of appetite-suppressive medications to treat hunger[5]. From here, Atkin’s developed his diet plan, focussing on ‘eating right’ rather than on the conventional wisdom to ‘eat less[5].’
The Atkin’s diet is a more prescriptive diet than classical keto, in that there are 4 phases that need to be followed[6].
The Atkin’s diet instructs participants to initially eliminate almost all carbs.
(Phase 1) Induction
Atkin’s recommends a 2-week induction phase, where carbohydrates are limited <20g, in order to induce a state of ketosis. Here, fat can be consumed freely and protein intake is also encouraged, with no restriction on caloric intake[6].
(Phase 2) Ongoing Weight Loss (OWL)
During the OWL phase of the diet, participants slowly add 5g of carbohydrate per day to their diet, while continuing to lose weight. When weight loss slows, the level of carbohydrate is not increased further, but sustained until the goal weight is achieved[6].
(Phase 3) Pre-maintenance
After goal weight has been achieved, additional carbohydrates from whole foods can be slowly introduced, such as fruits and vegetables. Carbohydrates continue to be slowly added until weight gain occurs.
During this phase, carbohydrate intake is approximately 50-80 grams for a 2000kcal diet[6].
(Phase 4) Maintenance
The previous 3 phases have primed the body and provided a good idea about how many carbohydrates an individual can tolerate before gaining weight.
Ideally, the maintenance phase will be for life, and normally ranges from about 80-100g of daily carbohydrates[6].
Side effects
The most common side effects of Atkin’s occur during the initial phases and tend to subside shortly thereafter. Gastrointestinal symptoms were most commonly reported, and other side effects include;
- Diarrhea
- Constipation
- Nausea
- Headaches
- Changes in vision
- Leg cramps
Side effects are typically mild, many of which can be greatly reduced through sodium supplementation[6].
Carnivore diet
Macronutrient split: 100% Fat + Protein | Trace amounts of Carbohydrates
Overview
The Carnivore diet is a plant-free diet that has recently been gaining traction, partly due to celebrity advocates, such as Joe Rogan, who has discussed it a number of times on his popular JRE podcast[7].
Carnivore is very simple, eliminating all foods but animal-derived proteins and fats.
It is not uncommon for people following the carnivore diet to consume red meat daily, and typical meals consist of meat, poultry, seafood and eggs.
The carnivore diet is very recent, and as such, there is limited published literature concerning the health benefits or concerns[7].
Self-reported progress has however shown extreme weight loss and there are unsubstantiated claims that carnivore helps with autoimmune conditions.
Side effects
Data regarding side effects is sparse, although a paper that conducted a large survey of people following the carnivore diet found that the most common side effects included[7];
- Diarrhea
- Constipation
- Muscle cramps
- Dry skin
- Hair loss
The carnivore diet is a more extreme low carbohydrate diet that is still in its infancy. The coming years will see if it is here to stay or a transient diet fad.
Paleo diet
Macronutrient split: 35% Fat | 30% Protein | 35% Carbohydrate
Overview
The Paleo diet is by definition, a moderate diet.
It consists of a moderate amount of fats, proteins and carbohydrates and is not a typical low carbohydrate diet[8].
The diet is based on foods that would have been available to our hunter-gatherer ancestors, and by following this way of eating, is thought to bring about improvements in overall health and the absence of disease[8][9].
Paleo consists of lean meats, seafood, eggs, fruit, nuts and low carbohydrate vegetables[8]. It is possible to follow a modified version of the diet, by actively choosing foods that are lower in carbohydrates, but still in line with the overall philosophy of the diet.
Like many other low carbohydrate diets, the emphasis is not on calorie tracking, but more on choosing healthy whole foods (with a low glycemic index) that would have been readily available before the arrival of organised agriculture[8].
Side effects
Similar to other low carbohydrates, Paleo often has minor side effects which tend to subside after the body has acclimatised to the new way of eating[8][9]. Side effects commonly include;
- Lack of energy
- Headaches
- Difficulty focussing
- Diarrhea
- Constipation
From talking to Paleo adherents through social media channels, it seems that sudden changes in diet tend to cause the most notable side effects, suggesting a more gradual progression into the diet may be warranted.
Conclusion
Low carbohydrate diets have been increasingly represented since the 1970s, and have been popularised largely due to their weight loss results.
As described above, there are numerous variations, some of which offer greater flexibility than others.
With all this information, it can be confusing to know where to start. Ultimately, the correct diet for you will vary depend on your personal goals, circumstances and how your body responds.
