Shaun Ward MSc ANutr
What Is A Low-Carb Diet?
As the name suggests, a low carbohydrate diet is where an individual purposely restricts themselves from consuming carbohydrate-based foods.
Foods high in carbohydrates (sugar, bread, pasta, rice) are limited, or replaced with foods that predominantly contain protein and dietary fat (meat, fish, dairy, eggs, nuts, and seeds). Foods are also allowed if they are carbohydrate-based, yet contain minimal carbohydrates based on the total volume of the food (low calorie options), specifically regarding green vegetables and some fruits.
Although world health organizations still promote a predominantly whole-food carbohydrate-based diet (~50% carbohydrates), they have also stated that current intakes at a population level need to be lowered. In addition, they also advise that refined carbohydrates should be restricted whenever possible, and should be replaced with either unsaturated fats or wholegrain products.
Who Is This Diet For?
There are multiple different reasons why people choose to follow this eating plan:
Minimizing carb intake suits those who are unable to tolerate large amounts of carbohydrates, especially pre-diabetics, as they may cause large fluctuations in blood glucose and result in energy ‘crashes’.
Low-carb diets have also been linked with improved blood lipid profiles, insulin sensitivity, and reduced inflammation.
However, the main reason for low-carb diet plans is undoubtedly their role within weight loss, as it is assumed that when carbohydrate availability is significantly reduced the body will be forced to maximize fat oxidation.
What Defines ‘Low Carbohydrate’?
Unfortunately, a true definition to what classifies as ‘low carbohydrate’ is severely lacking, with contradicting definitions throughout scientific studies which complicate the research in this area.
Some sources will define a low-carbohydrate diet as restricting carbohydrate intake to 20-60 grams per day (similar to a Ketogenic diet), while others suggest anything below 40% of total calories from carbohydrate can be considered low.
For the purpose of this review, ‘low carbohydrate’ will be deemed between 10-30% of total calories from carbohydrate.
The minimum requirement of 10% total calories from carbohydrate has been placed to distinguish the differences between a "low" and a "very low" carbohydrate diet.
It's Not The Same As A Keto Diet
A common misconception when following a low-carb diet is that this will automatically put someone in a state of ketosis.
Ketosis is a metabolic state in which most of the body’s energy supply is derived from ketone bodies in the blood, in contrast to a normal state of glycolysis where glucose (from dietary or stored carbohydrates) provides most of one’s energy.
Ketosis occurs when the body is metabolizing dietary fat or stored body fat at an extremely high rate and converting the fatty acids into ketones; an alternative fuel source.
However, there is a maximum threshold of carbohydrates that can be consumed for ketosis to occur, and this is usually only achieved by no carbohydrate, or very low carbohydrate eating programs.
A low-carb diet (10-30% total calories) likely provides enough carbohydrates to avoid a metabolic state where ketones are produced at any considerable rate.
This being said, there is no present consensus as to the carbohydrate ‘cut-off limit’ to induce ketosis, which will vary on an individual basis, although intakes below 50 grams per day are generally reported to cause ketosis.
Is This Diet Effective For Weight Loss?
Similar to any eating plan that focuses around the restriction of one or more food groups or nutrients, a low carbohydrate approach is effective at weight loss.
Due to the restrictive nature of the diet, even individuals following a low-carb diet without placing additional restrictions on food quantity still generally experience weight loss, at least in the initial stages.
Low carbohydrate advocates will promote that weight is lost due to the reduction of circulating insulin levels, which promotes the degradation of stored body fat.
However, as dietary fat intake is greater than other diets, there will also be more fat storage throughout the day to counteract the increased release of body fat. In other words, although more body fat is being released into the blood stream, it is not necessarily being utilized for energy at a higher rate than higher carbohydrate diets. The net balance of body fat release versus body fat storage will remain similar to other diets, and is ultimately dependent on daily energy balance and calorie intake.
Studies that implement this diet have consistently resulted in significant weight loss:
- 3% body weight loss after 12 months .
- 8lbs loss after 12 weeks .
- 4lbs in 10 weeks .
- 2lbs in 8 weeks .
- 2lbs in 12 weeks .
Based on these studies, low carbohydrate approaches lead to an approximate 1.0-2.2lbs bodyweight loss per week, although this will depend on an individual’s body weight, body fat percentage, and total calorie intake.
Induction of initial weight loss with this diet is fully explained by a reduction in overall caloric intake and by reduced carbohydrate (glycogen) and water stores in the muscle and liver.
The lowered calorie intake likely puts an individual in a state of negative energy balance – consuming less energy than expended per day – which forces the body to utilize stored energy, including body fat, to make up for the difference in energy that is not available through food.
The reduced glycogen stores will also affect weight loss as each gram of glycogen is stored with ~2-3 grams of water, causing a sudden drop in water weight. However, depending on the rate of glycogen depletion this process will become stagnant after 1-2 weeks.
In this respect the loss of glycogen and water is not a true measure of weight loss, as their stores will be replenished once the diet is stopped.
This is also why the amount of weight lost in individuals who follow either a high carbohydrate or a low-carb diet for one year, assuming calorie intake is the same, is not significantly different, as the water losses and body water content after long periods seems to become similar .
It is noteworthy that the reduction in overall calorie intake may also be due to other reasons, as opposed to purely a restriction of food choice, mainly regarding the diets effect on hunger and satiety levels.
The increased protein intake that typically occurs on a low carbohydrate diet will subsequently decrease hunger and reduce energy intake as protein is the most satiating macronutrient when measured calorie-for-calorie with dietary fat and carbohydrate. This is due to its effect on sensory and cognitive signals that determine satiation.
Hunger levels may also be reduced from the slight initial increase in circulating ketone bodies, which have demonstrated to exert an appetite suppressant effect via reducing neuropeptide hormones, such as ghrelin, which signal hunger .
The Potential Benefits of The Low-Carb Diet
Below we've listed the scientifically-proven health benefits of this eating program:
Most of the benefits of a low carbohydrate intake are because of the decrease in sugar and refined carbohydrates. A lot of research suggests sugar has an integral role in the development of inflammation, diabetes, hypertension and certain cancers.
Sugar intake is partially responsible for the synthesis of free fatty acids in the liver, which triggers inflammatory processes and the formation of harmful reactive oxygen species.
It seems the recurrent hyperglycaemic responses from repeated carbohydrate ingestion (mainly refined carbohydrates) results in an overproduction of free radicals and release of proinflammatory substances that induce inflammation and cause vascular damage .
In addition, high sugar diets may lead to intestinal bacterial overgrowth and increased intestinal permeability, which can disturb gut function and the immune system which consequently worsens inflammation and risk of disease .
The reduction in sugar can also be of benefit to diabetic patients who need specialized control for their insulin and blood sugar levels. Low-carbohydrate diets may even reduce the necessary insulin doses (injected) in type 2 diabetics by ~50% within the first few weeks.
This diet can reduce the risk of cardiovascular disease by improving blood pressure and lipid disorders that may cause the formation of fatty deposits in the arteries.
These improvements are due to an increase in HDL-cholesterol levels – responsible for transporting cholesterol out of cells - and a decrease in plasma fatty acids.
Moreover, it may reduce cardiovascular risks by significantly decreasing several biomarkers of inflammation, which are pivotal in the pathogenesis of arterial plaque formation.
Weight Loss May Be The Driver
Low carbohydrate diets do result in improvements in blood glucose levels, insulin sensitivity, and blood lipid profiles, however this is largely due to the beneficial effect weight loss has upon these factors.
It has been found that the diets health benefits are principally associated with the decreased caloric intake and increased diet duration as opposed to the reduced carbohydrate content.
In fact, body weight itself is known to be the main driver in effecting inflammation and disease risk.
At present, the negative findings on sugar intake appear to be confounded by excessive energy intakes; consuming more calories than expended. As obesity and high sugar intakes often co-exist, it is certainly possible that weight gain is a potential mediator in the association between sugar intake and inflammation.
However, despite sugar not being proven to necessarily have damaging effects in moderate quantities, the avoidance of its intake can only be praised when reviewing the efficacy of the diet.
What Are The Risks?
Like anything, there are also some potential risks that you should be aware of:
Less Favorable Health Changes Than Balanced Diets
Interestingly, low-carbohydrate diets result in less favorable changes in LDL-cholesterol than higher carbohydrate diets, despite both usually having some type of improvement from weight loss.
Recent evidence suggests the healthiness of the diet, separate from weight loss, is dependent on the amount of animal products included in the diet. Specifically, low carbohydrate approaches that utilize high intakes of meat (lamb, beef, pork, chicken) are associated with higher chronic disease and mortality risks compared to moderate carbohydrate protocols (50-55% carbohydrates) .
Low intakes of fruits, vegetables, and whole grains may further worsen the risk for chronic diseases.
Accordingly, it is suggested that there is insufficient evidence to specially recommend low carbohydrate diets rather than isocaloric, alternative diets .
It appears that the health effects of the diet may depend on the type of protein and fat consumed, and the amount of fruit and vegetables included. Those looking to follow the diet for any appreciable length should ensure they include as many vegetable sources of protein and fat as possible, and not let animal products take up the majority of the diet.
Potential Nutrient Deficiencies
Another key negative with a low carbohydrate approach is the increased risk of nutrient deficiencies due to the enforcement of food choice restriction.
The generally low consumption of fruits, vegetables and whole grain products during low carbohydrate diets consistently seems to reduce the overall intake of dietary fiber, vitamins, calcium, potassium, magnesium, iron, as well as other bioactive compounds and phytochemicals.
Unsurprisingly, this has led to review studies on diet quality finding that high-carbohydrate diets (>55% total calories) give the highest dietary adequacy scores, whereas low-carbohydrate diets (<30% total calories) produce the lowest dietary adequacy scores .
Although it cannot be confirmed, the nutrient deficiencies may be the reason why some studies report high drop-out rates and adverse effects such as dehydration, headaches, gastrointestinal symptoms and vitamin deficiencies .
Low-carb diet plans are those that restrict consuming carbohydrate-based foods, however should not be consumed with the Ketogenic or Atkins diets which are very low carbohydrate.
As the program is restrictive, those on a low-carb diet will generally experience weight loss, especially in the initial stages. The weight loss is as a result of an energy reduction, not as a result of lowered insulin production.
Low carbohydrate diets will often lead to reduced inflammation and improved blood lipid profiles due to the weight loss, couple with the removal of sugar and refined carbohydrates.
However, the changes in lipid profiles may not be as favorable compared to higher carbohydrate diets with the same caloric intake. This is likely due to the increased saturated fat and dietary cholesterol intake from low carbohydrate protocols.
They may also lead to nutrient deficiencies due to the restriction on fruits and wholegrains.