Why do people go on diets?
There are numerous reasons to take up a diet including becoming more healthy, improving mood, increasing lifespan and overall having more energy. But if we’re honest, the main reason people go on diets is to lose weight.
Table of contents
Reduction in appetite due to the higher satiety effect of proteins
Appetite suppressing effects of reduced insulin levels
Overall increased energy expenditure
Keto leads to successful weight loss
Keto vs low-fat
Low calorie keto
Low calorie keto vs low calorie alone
Keto-induced weight loss is well documented
The keto diet and other low carb diet variations (e.g. Atkins) have proven extremely popular due to their reported success in inducing weight loss.
Weight loss has often been reported to be more rapid than on other diets, as well as reducing the need to track calories.
The internet is filled with anecdotal experiences of successful weight loss journeys, that credit keto for their success, but what does the science say about it?
Following Keto leads to successful weight loss
Keto is better than low-fat for weight loss
Numerous studies have demonstrated the weight loss benefits of keto.
Strong evidence comes from a meta-analysis of 13 studies including 1577 participants, in which keto diet adherence was used as an interventional tool[1]. The review assessed the effectiveness of keto vs low fat diets in leading to weight loss.
Across the studies, the participants on the keto diet achieved significantly greater weight loss results compared to those that followed a low-fat diet[1].
This held true for all sub-group analyses, except for those with a 24 month follow-up period. This could indicate that over the longer term, the effectiveness of keto wanes, but this needs to be further investigated before arriving at any conclusions.
Low calorie keto is even more effective for weight loss
Perhaps more significant, when combined with a low calorie intervention, keto can be even more effective.
An observational study utilising a very low calorie keto diet (VLCKD) in patients with obesity and mild kidney impairment found that keto was a highly effective tool at inducing weight loss[2].
The study included 92 participants who adhered to the VLCKD for a period of 3 months. After the study period, the average weight loss was approximately 20% of initial weight, demonstrating an extremely effective rate of weight loss[2].
It is important to note however that this was an observational study, and the combination of keto and a very low calorie diet means it is difficult to identify if the low calorie or the keto approach was chiefly responsible for the weight loss[2].
Keto leads to more weight loss than low calorie alone
Interestingly, it appears that a reduction in calories is not the only factor that leads to weight loss.
A study that examined the effects of a low calorie keto diet vs a normal low calorie diet in patients with type II diabetes and a BMI 30 – 35 found that the low calorie keto diet was more effective[3].
After 4 months, participants over 85% of the participants on the keto diet experienced a weight loss of more than 10% compared to baseline[3].
Weight loss and waist circumference changes were both significantly greater in low calorie keto compared to the low calorie diet alone[3].
This implies that keto leads to physiological changes that accelerate weight loss, compared to calorie deprivation alone.
Keto is thought to lead to weight loss through a number of different mechanisms
Following a Keto diet undoubtedly leads to weight loss, but the exact mechanism for this is more difficult to understand.
A number of mechanisms have been proposed by which keto leads to weight loss, although most of these still lack strong conclusive evidence[4].
1. Reduction in appetite due to higher satiety effect of proteins
Protein consumption leads to increases in satiety peptides
A common explanation for the weight loss effects of keto is improved appetite control, due to the higher satiety effect of proteins compared to carbohydrates.
There is a debate between the satiating effects of fats compared to carbohydrates, with carbohydrates generally being regarded at better for appetite, given their lower energy density compared to fats.
It is however quite clear that the consumption of protein leads to higher levels of satiety, leading to reduced overall caloric intake, resulting weight loss[5].
It is thought protein consumption leads to increased suppression of certain hormones and increases in satiety peptide concentrations, including glucagon-like peptide-1 (GLP-1), cholecystokinin (CCK) and peptide YY (PYY)[6].
These hormonal changes, combined with other factors associated with higher protein diets, lead to greater weight loss[6].
Keto leads to reduction in ghrelin
The influence of hormonal changes in regulating appetite is complex, but we know that the hormone ghrelin is responsible for increasing appetite and stimulating the secretion of growth hormone[7].
Reductions in ghrelin have been shown to have a suppressive effect on appetite and this has been demonstrated in a number of studies with participants on keto[8].
Perhaps more significant, is the longer term hormonal changes that occur when the body has lost a significant proportion of weight.
Studies have found that weight loss induces increased secretion of ghrelin and corresponding increases in appetite.
In contrast, a study conducted in obese participants on keto found that although there were increases in ghrelin after weight loss, this was only a transient increase up to 3 weeks, after which it did not increases further[9].
High carb diets lead to increased appetite
In addition, people on keto diets benefit from decreased ghrelin levels due to reduced carbohydrate intake.
One study found that after high carbohydrate breakfast, there is an increase in active ghrelin levels[10].
Notably, this also leads to increased intake at lunch compared to controls. The study specifically found that in obese girls, a combination of a high fat and high carbohydrate breakfast increased ghrelin secretion and lead to increased intake of food in subsequent meals[10].
This supports the idea that eliminating or greatly reducing carbohydrates from your diet, due to keto, could result in reduced hunger signals.
This could help to explain why many people find it easier to lose weight on keto, and continue to lose weight after the initial period of weight loss.
2. Appetite suppressing effect of reduced insulin levels
Insulin resistance alters satiety signalling
Many people who start on keto are obese or overweight.
In obese and significantly overweight individuals, it is common to have a condition called insulin resistance.
This means their body no longer adequately responds to insulin signalling[11].
This is relevant because in normal healthy adults, insulin can have a satiating effect. In obese individuals, it can have the opposite effect, and lead to increased appetite[11].
Following consumption of a meal, levels of glucose increase in the bloodstream. This glucose needs to be taken up by cells so that the energy may be utilised, and this process is facilitated by the secretion of insulin[11].
If Insulin levels are consistently too high, the body becomes less efficient at moving this glucose into the cells[11]. This results in impaired insulin signalling, and triggers overconsumption of carbohydrates[11].
Carbohydrates may not be as satisfying in people with insulin resistance
A number of studies have demonstrated that insulin leads to increased food intake in obese individuals.
This is due to the high insulin levels following food consumption, leading to a compensatory hypoglycaemic response, which ultimately leads to further food consumption[12][13][14].
In addition, the secretion of insulin may not adequately stimulate satiety centres of the brain in individuals with insulin resistance[12].
This means foods with high insulin responses (carbohydrates) may not be as satiating in individuals with insulin resistance, which leads to over consumption.
By restricting carbohydrates, levels of insulin remain low (insulin levels are highest for carbohydrates-rich meals) and steady, leading to an improved insulin resistance profile.
This improved insulin profile is thought to lead to reduced hunger signals and greater satiety, resulting in improved weight loss[12].
3. Overall increased energy expenditure
Glucose is the primary fuel in the body, and when this runs out, the body switches to breaking down glycogen from the liver into glucose, in a process called glycogenolysis[15].
After glycogen stores have run out, the body then starts to convert non-carbohydrates (amino acids and lactate from protein, and glycerol from adipose tissue) into glucose in a process called gluconeogenesis[15].
Gluconeogenesis is an energy-demanding process, and the increased energy expenditure may contribute to weight loss experienced on ketogenic and other low carbohydrate diets.
Keto leads to increased energy expenditure through gluconeogenesis
This is strengthened by a study that tested the effect of a high protein, low carbohydrate diet on energy expenditure and gluconeogenesis.
When fed a diet low in carbohydrates and high in protein (30% : 70%, protein : fat), participants had increased gluconeogenesis and higher resting metabolic rate (energy expenditure) compared to participants who ate a normal western diet (12% : 55% : 33%, protein : carbohydrate : fats)[16].
Interestingly, 42% of the increased energy expenditure was explained by the increase in gluconeogenesis[16].
This supports the position that an increase in energy expenditure contributes to the weight loss effects of keto.
It is however worth noting that this was a small study (10 healthy male participants) and the subjects were assessed after 3 days on the diet[16].
As a result, it is unknown if this increase in energy expenditure is short-term or represents an increased metabolic rate over the longer term.
Keto-induced weight loss is well documented
Successful weight loss due to following a Keto diet is well documented.
A number of different mechanisms are thought to contribute to this, but precisely how much each factor contributes to the overall weight loss experienced is currently unclear.
Additional studies are still needed to demonstrate whether keto has superior results over the long term, but from the current data, keto is a good option for obese and overweight individuals looking to lose body fat.
