Low carb diets, keto, Atkins…we have all heard about these dietary patterns, but what are the implications for our health? And is a low carb diet healthy?
What is a low carb diet?
Low carbohydrate diets have been around for several decades, however as of late they have surged in popularity. In fact, with the rise of overweight and obesity, the public is eager to find solutions to their expanding waistlines.
There is no governing authority that regulates or defines what constitutes a low carb diet. However, for context, the typical western diet provides 50% of energy from carbohydrates, 35% of energy from fat and 15% of energy from protein. In comparison, a high fat low carb diet can provide 60% of energy from fat, 10% from carbs and 30% from protein.
The low carb pioneer
But perhaps the most famous low carbohydrate diet, considered the pioneer of the low carb movement, is the Atkins diet.
In 1972, Dr Atkins released his book titled the Dr Atkins’ Diet Revolution which sold millions of copies worldwide. The Atkins diet is divided into four steps. Firstly, there is a two-week induction period during which you restrict carbohydrates to less than 20 grams/day. The diet recommends moderate protein intake from animal foods such as beef, chicken and eggs, and fat intake is unlimited. Moreover, during this phase, you are not allowed bread, grains, fruit and starchy vegetables. Further, you are not permitted dairy products with the exception of cream, cheese and butter (due to their low carb, high fat content).
Throughout the following stages, carbohydrate restriction is eased until the individual can determine the amount of carbohydrate required to maintain weight loss. This level varies widely amongst individuals and could be anywhere between 25 grams/day up to 90 grams/day depending on body weight, physical activity and other factors. Moreover, the diet encourages followers to check their urine for ketone bodies to ensure they are in ketosis.(1)
Ketosis…
When following a low carb diet, one of the typical bodily consequences is ketosis. Ketosis refers to a bodily process that occurs when our carbohydrate intake is limited. In fact, when our body is faced with low carb intake, it utilises our glycogen stores which are broken down into glucose to use as fuel. The liver and muscles are the primary glycogen stores in the body. However they are finite stores and within 24 to 48 hours of dietary carbohydrate restriction, they become depleted.
Furthermore, a characteristic of glycogen is that it binds to water. Therefore, this explains why during the first week of a highly carb restricted diet such as Atkins, many people achieve “weight loss”. However, this is due to water loss as opposed to fat loss. Loss of glycogen and water does not truly reflect weight loss because once the diet ends, these stores will be replenished. However, if the diet continues and we do not replenish glycogen stores, the body starts to utilise its fat stores. Therefore, our body releases fatty acids into the bloodstream and the liver utilises them to produce energy.
And ketone bodies
When the liver partially oxidises fatty acids, it produces a compound called acetoacetate which is then converted into b-hydroxybutyric acid. Together, we refer to these compounds as “ketone bodies”. Our kidneys filter ketone bodies causing an increased loss of sodium and water. The maximum amount of carbohydrates required to induce ketosis varies between individuals. However, typically it equates to less than 20% of total energy intake.
There are very few studies observing the long-term health effects of ketogenic diets. However, commonly reported side effects include dehydration, gut issues, vitamin deficiencies and low blood sugar. Moreover, long-term ketosis leads to increased levels of uric acid in the blood. Long-term high levels of uric acid could be linked to kidney and joint complications.(2)
Related reading
“Long-term ketosis leads to increased levels of uric acid in the blood [which] could be linked to kidney and joint complications.”
Cardiovascular effects
By definition, most diets that result in weight loss will lead to positive outcomes on blood lipid profiles. Typically, studies report reductions in total cholesterol and triglycerides. However, the nutritional composition of calorie restricted diets can have varying effects on blood lipids. For example, people following diets that are low in saturated fats report greater decreases in “bad” LDL cholesterol.(2)
However, low carb diets are typically higher in saturated fats due to a higher consumption of animal products compared to standard low calorie weight-loss diets. Therefore, long-term intake of high levels of saturated fats may negatively impact blood lipid profiles and increase the risk of cardiovascular complications.
Low carb diets and bone health
Low carb diets may potentially impact bone health. The science regarding the role of calcium intake in bone health is robust. In fact, calcium in the diet is essential in building and maintaining bone mass and reducing bone loss throughout all life stages, from childhood into the later stages of life.
However, many low carb diets restrict the intake of dairy, mainly milk and yoghurt due to their carbohydrate content. However, these dairy sources are the main sources of dietary calcium for most people. Peak bone mass is a determining factor in the risk of developing fractures and osteoporosis. In fact, we achieve peak bone mass early in life.
Therefore diets that restrict calcium intake, especially in people under the age of 30, can hinder optimal acquisition of peak bone mass. Thus, the risk of developing osteoporosis later in life may increase in such individuals.(3)
Low carb as a solution for obesity?
Low carb diets are often recommended as a solution for overweight and obesity. However the literature is conflicting regarding the efficacy of such diets on long-term sustainable and healthy weight loss. One group of researchers conducted a systematic review of the published literature observing the effects of low carb diets versus control diets (either low fat or energy restricted) in adult populations with overweight or obesity. The study found that amongst the highest quality meta-analyses, there was little difference regarding efficacy between low-carb and control diets. Moreover, the larger the sample size, the smaller the differences in weight loss between test and control groups.(4)
Overall, we require higher quality reviews and randomised controlled trials before recommending low carb diets as the gold standard for weight loss over other energy restriction approaches.
Low carb vs low fat in the short-term…
Whilst low fat diets were once touted as the key to weight loss, the media and popular fad diets of today advertise low carb diets as the secret to unlocking fat loss. But what are the differences between the two and how do they compare when it comes to weight loss?
A randomised trial in healthy women looked at the effects of a very low carbohydrate diet on body weight and cardiovascular risk factors compared to a calorie-restricted low fat diet. The study’s subjects followed either a very low carb diet ad libitum or a calorie restricted diet with 30% energy from dietary fat. Both groups followed their respective diets over a period of 6 months.
It was found that the very low carb diet group lost more weight and more body fat than the low fat diet group. Moreover, at baseline prior to the study, mean levels of blood pressure, lipids, blood glucose and insulin were within normal ranges across both groups. Moreover, all of these parameters improved throughout the study, however there was no significant difference between the two diet groups after 6 months.
Overall, the study concluded that a very low carb diet is more effective than a low fat diet for short-term weight loss. In addition, in healthy subjects, it is not associated with negative effects on cardiovascular risk factors.(5)
However these findings are specific to short-term intervention in healthy individuals in one study group.The long-term effects of such restrictive low carb diets in individuals with health complications are yet to be confirmed.
…and in the longer-term
Moreover, a meta-analysis of randomised controlled trials observed the effects of low fat diets vs low carb diets on weight loss and cardiovascular risk factors. The study included over 440 individuals with a BMI of at least 25 (i.e. participants were overweight or obese). The researchers found that after 6 months , the low carb diet groups had lost more weight than the low fat diet groups, however after 12 months this difference was no longer seen. Moreover, triglyceride and HDL cholesterol values were more favourable in subjects in the low carb diet groups. However, total cholesterol and LDL cholesterol values were more favourable for people in the low-fat diet groups.(6)
Overall, low carb, non-energy-restricted diets appear at least as effective as low fat, energy-restricted diets for weight loss for up to 12 months. However, potential favourable changes in triglyceride and HDL cholesterol levels should be compared to potential unfavourable changes in LDL cholesterol levels when low-carb diets for weight loss are considered.
Weight loss and genes
Obesity is one of our century’s greatest public health challenges. Consequently, many strategies have been tried and tested for weight loss. Amongst these, a common rivalry has been between the low fat diet defendants and the low-carb diet supporters. Most studies have found modest weight loss after 12 months and insignificant differences between the two diets in terms of efficacy. However, individual weight loss varies widely within diet groups, suggesting that some people respond better to certain dietary approaches than others. In fact, there is no universal one-size-fits all diet for weight loss. Different people respond to different strategies.
Nonetheless, science is yet to understand the reason for interindividual differences. One hypothesis is that genetic variation may predispose people to different weight loss that varies based on diet type. One study found that people with a “low fat responsive genotype”, essentially determined by specific gene patterns, lost more weight when assigned to a low fat diet than when assigned to a low carb diet. Conversely, the opposite was true for people with a “low carb responsive genotype”.(7, 8)
The DIETFITS study
The main objective of the Diet Intervention Examining The Factors Interacting with Treatment Success (DIETFITS) study was to trial whether a set of 3 different genotype patterns or baseline differences in insulin secretion (the blood insulin concentration at 30 minutes after a glucose challenge) or both, predisposed subjects to differences in weight change over 12 months while on a low fat vs a low carbohydrate diet.(9)
The researchers conducted their tests in over 600 overweight adults and found that weight change was not significantly different between the two groups after 12 months and there was no observed diet-genotype or diet-insulin interaction with weight loss.
Overall, the findings suggest that there is no superior strategy to weight loss and that dietary changes are key to successful weight loss.
Thinking sustainably
In conclusion, it appears that in the short-term, for healthy individuals, low-carb diets do not pose any major health concerns and can be a tool for weight loss. However, long-term adherence to a low-carb diet may increase the risk of metabolic diseases in part due to unfavourable changes in lipid profiles. In addition, low carb diets may compromise bone health and lead to nutritional deficiencies in some cases.
Moreover, if you choose to follow a low carb diet in the short-term, care should be taken to contrast potential side-effects. For example, water intake should increase to prevent dehydration and you should ensure that you are consuming enough fibre and calcium which are often lacking in low carb diets.
In any case, we recommend talking to your dietitian before starting a low-carb diet because it may not be suitable for your individual needs and health status.
