How Low Carb High Fat (LCHF) Diet Affects Your Metabolism and Weight Loss
Low Carb High Fat or LCHF diets are gaining popularity. From fat loss, energy boost, neuroprotection, and alertness – pick your weapon. But is this weight loss sustainable? How does Keto Diet affect your metabolism? What about Thyroid Hormones on a High-Fat diet?
The ketogenic diet promotes a shift in metabolism from glucose to fats, promoting fat loss, metabolic function, and supporting energy levels through nutritional ketosis. Training the body to metabolize fats can exert a metabolic reset, with benefits extending to cognition and aging, dependent on increased energy efficiency.
What is Keto Diet?
The ketogenic diet is a high-fat, low-carbohydrate diet designed to shift the body’s use of fuel from glucose to fats. It is characterized by severe carb reduction, consuming below 50 grams per day, which is around 5-10% of total calories for most. Fats make the larger portion of total calories at 70-80%, then protein fills the rest.
The keto diet tends to stimulate ketosis, a metabolic state which promotes fat-burning, training the body to start producing and using ketones for energy. The key goals of low-carb diets, which mainly work by switching the fuel source, include fat loss and improvements in cognition and metabolic function.
What is the rule for keto diet?
Reducing carbohydrate intake typically to <50 grams daily while increasing fat consumption and maintaining moderate protein intake, aiming to shift the body into a state of ketosis.
What foods do you eat on a keto diet?
On a keto diet, foods high in fat and low in carbs are preferred. Healthy fats include avocados, nuts, seeds, and olive oil. Protein rich foods like meat, fish, eggs, and dairy; and low-carb vegetables like leafy greens, broccoli, and zucchini.
Are keto diets healthy?
Keto diets can aid in improvements in metabolic health, neuroprotection, and weight loss. Typically, people who tend to overeat carbohydrates and have high insulin levels experience the greatest benefits. However, keto diet is very restrictive, metabolism-shifting, and definitely not for everyone.
What is LCHF Diet?
The Low-Carb, High-Fat (LCHF) diet is a broader and more flexible approach to reducing carbohydrate intake while increasing dietary fat. Unlike the keto diet, the LCHF diet doesn’t strictly aim for ketosis, so carb intake can range from moderate to low (50–150 grams per day), depending on individual goals. Fat intake is emphasized, and protein is consumed moderately.
For most sedentary people who overconsume carbohydrates, reducing the total amount of simple carbohydrates can be quite beneficial. It decreases the metabolic strain on the body, improving metabolic function, body composition, and insulin sensitivity. In terms of reducing carbohydrate intake, the LCHF diet is a less intense and more convenient approach for many, compared to keto.
Are keto and LCHF the same?
Keto is a type of low-carb, high-fat (LCHF) diet with stricter carb restrictions aimed at achieving ketosis, while LCHF diets are more flexible and may not necessarily induce ketosis. Carb-reduction is the main trait in both.
Can you lose weight on a low carb high fat diet?
Yes. Low-carb diets have proven to be effective for reducing waist circumference, promoting weight loss, and fat loss. Initially the higher weight loss is due to water loss, but improvements in metabolic efficiency lead to sustainable weight loss, making low-carb an effective strategy.
Metabolism: Fats vs. Carbs
To sustain survival, the body requires calories which can come via fats or carbohydrates, as a predominant energy source. Neither shows absolute superiority. Generally, the ability to shift between glucose and ketones, so called metabolic flexibility, is associated to better metabolic health. Since most tend to prioritize carbs in their diet, metabolic flexibility is achieved mainly via carb-restrictive approaches like keto, LCHF, fasting, or calorie restriction. (1) (2) (3)
Carbohydrates are the primary source of fuel for the body and brain. They’re superior to fats for faster energy creation, particularly fueling intense, anaerobic exercise. (4) (5) (6) The body stores glycogen in the muscles and liver which one breaks down when the need of quick energy arises.
Fats are more energy efficient. Per the same amount of fats, one can create more molecules of ATP, slower. The body breaks down fats into FFAs and glycerol, transporting FFAs to the mitochondria where beta-oxidation occurs. After a series of reactions in the Krebs cycle, energy is created in the electron transport chain (ETC). (7) A slower yet more sustainable way to create energy for low-intensity purposes like daily functioning, cognition, or walking.
The data suggest that flipping the metabolic switch is key to improving fat loss and metabolic function. This is the body’s shift from creating glucose-based energy, to running on ketones for fuel, which the body and brain prefer during fasting, exercise, and low glucose states. (3) (8) (9)
How do I reset my metabolism to lose weight?
Reset is a fancy term. It’s used to describe improved metabolic efficiency, which depends on fat oxidation that happens during ketosis. So a good way to “reset” one’s metabolism and stimulate a metabolic shift is reducing carbohydrate intake, exercising, or extending the fasting window.
In what order does your body burn energy?
Your body burns energy in this order: carbohydrates (as glucose), fats (as fatty acids or ketones), and proteins (as a last resort, breaking down muscle for amino acids). High-intensity exercise will primarily burn glycogen; the lower the intensity, the more the body shifts to fat metabolism.
What are signs of fast metabolism?
Signs of a fast metabolism include feeling hungry often, difficulty gaining weight, higher energy levels, frequent bowel movements, and a warmer body temperature.
Benefits of Low Carb Diet
Reducing carbohydrate intake is linked to improved metabolic health, weight loss, energy levels, and mental clarity. Partially, these effects stem from
- reducing total calorie intake
- reducing total glucose intake
- reducing elevated insulin levels
- reducing consumption of high-GI foods.
Since most of the population tends to be in the so-called anabolic window or high insulin state, glucose deprivation flips the metabolic switch starting a chain of catabolic reactions of cellular repair.
Metabolic Function
Metabolic function is the ability to extract sufficient energy from nutrients. That energy can be dominantly derived from either fats or glucose.
Overrelying on carbohydrates as an energy source can lead to metabolic disruption, particularly when refined, simple, high-GI foods are overconsumed. (10) This loop of fatigue and weight-gain further contributes to inflammation, carving a path for obesity and diabetes, increasing the risk of metabolic syndrome. Partly that is dependent on hunger signalling, fat cells dysfunction, and metabolic strain, most of which depend on carbohydrate overload. (11) (1) (12)
Reducing carbohydrate consumption therefore allows the body to tap into fats for fuel. This metabolic shift reduces the strain on the pancreas, lowering insulin and blood glucose levels which improves energy creation and tackles the underlying problem of overeating, being tired.
Numerous studies repeatedly show the link between low-carb diets or fasting and improved (13) (14) (15) (16) (17)
- metabolic function
- insulin sensitivity
- fasting glucose
- lipid profile
- fat loss and weight loss
- inflammation
- mitochondria function
Such alterations in metabolism make fat loss more efficient, making weight management easier, relative to energy levels. So far, the evidence is relatively strong suggesting that intermittent use of calorie or carbohydrate restriction greatly affects body composition, preventing weight gain, one of the primary drivers of metabolic syndrome.
Weight Loss
The simple formula for weight loss is calories in < calories out. Typical calorie deficit preferred for weight loss is about 300 kcal daily. This can result in 0.27 kg fat loss weekly, or 0.6 lbs. The body adapts to sustained calorie deficit by reducing metabolic rate.
Calorie = calorie is true in the short-term. But if a calorie from processed fat or refined sugar disrupts hormone signaling and contributes to fatigue, it’ll lead to weight gain eventually. So no, calorie ≠ calorie.
Improving metabolic function is key to sustainable fat loss, which is dictated by energy levels. Improving the body’s ability to derive energy from fats seems to be a great strategy.
The data shows keto and LCHF can promote significant weight loss, fat loss, reduction in waist circumference, and improvement in metabolic markers. (13) (16) (18)
Compared to high-carb diet, LCHF has proven superior producing a reduction of 1.5% body mass and 8.6% body fat in strength trained men. (19) Another meta-analysis including 6499 adults showed low-carb to be more effective for weight loss, HDL and TG levels, while low-fat had better outcomes for LDL and TC. (20)
Versatility and adherence are important in dieting. LCHF seems to be easier to stick to, presenting a more practical way to lose weight long-term. Although keto might prove superior short-term, due to various factors like hormonal imbalances and fiber deficiency, for many it’s not the best long term approach. (21) (22)
Cycling in and out of ketosis, done by intermittent keto diet or intermittent fasting can be a great way to train metabolic switching and gain most of the benefits associated with these catabolic diets.
Mitochondria Function
Mitochondria are the power cells that generate cellular energy via oxidative phosphorylation. They are vital for energy production, metabolic regulation, and cellular health. Improved mitochondria function is linked to longevity, as it helps reduce oxidative damage. Contrary, mitochondria dysfunction is linked to an increased risk of chronic diseases. (23) (24) (25)
Deriving energy from fats and exercising at a low to moderate intensity stimulates mitochondria function. Essentially, this triggers energy creation via respiration in the mitochondria.
Eating a diet low in carbohydrates is known to stimulate mitohormesis. As ketones levels increase, the body relies on mitochondrial respiration. During it, the mitochondria is creating moderate amounts of ROS to which they adapt, further improving their function. (26)
The data on keto, or keto-mimicking diets shows a potential for improving mitochondria function. Numerous studies, although some in animals, showcase keto’s potential to (27) (28) (29)
- increased mitochondrial respiration
- higher reliance on ketones
- lower oxidative stress and inflammation
- promotion of mitochondrial biogenesis
Mitochondrial biogenesis is the creation of new mitochondria. More mitochondria means more energy and slower aging, to an extent. The catabolic activity of such diets (LCHF, keto) stimulates AMPK and Sirtuin-1, both of which promote the expression of PGC-1α, enhancing mitogenesis. (27) (30)
Brain Function
Eating a diet low in carbohydrates may improve brain health and cognitive function, primarily relying on the use of ketones. Producing energy from fats creates less ROS and more ATP, which favors a healthier energy metabolism in the brain.
Neurodegenerative diseases partly stem from the inability to use glucose efficiently in the brain, and increased inflammation. Reliance on ketones attenuates these issues as ketones provide an alternative source to glucose and power up cognitive functions while reducing inflammation. (31) (32) (33)
By stimulating catabolic pathways, fasting or keto-mimicking diets can promote neural autophagy and contribute in toxin and amyloid plaque clearance in the brain. (34) (35) This shields neurons and preserves blood-brain barrier integrity, important for brain’s longevity.
Data in animals has also shown reliance on fats to significantly increase brain-derived neurotrophic factor (BDNF), a protein critical for synaptic plasticity, learning, and memory. (36) (37)
Lastly, brains fueled on fats may improve the balance of excitation in the brain. By modulating neurotransmitters like glutamate and GABA, it may reduce neurotoxicity and symptoms of anxiety.
A strategy known as metabolic switching has been proposed as a way to promote neuroplasticity, improve brain’s resilience, and slow cognitive decline. (38) Metabolic switching is engaging in intermittent periods of glucose abstinence, whether via fasting, keto, LCHF, or calorie restriction, to enhance metabolic flexibility.
Drawbacks of Long-Term Keto Diet
The short-term efficacy of the keto diet doesn’t grant long-term adherence, and comes with a few potential drawbacks. (39)
Nutrient deficiency can occur, largely due to the decreased intake of vitamins and minerals from plant-based foods. Phytochemicals, bioactive compounds, and antioxidants are also diminished, stripping the body of the protective components that fight oxidative stress.
Fiber deficiency is a common problem. Eating foods high in fats and protein like meat, avocados, and eggs only can impair gut microbiota diversity, starving the good gut bacteria. This poses a threat to gut health, affecting systemic inflammation and immunity.
The keto diet is also a low-adherence diet. Although short-term people may stick to it, most fall off the diet in a couple of months. There are numerous social and practical challenges that stand in the way of completely excluding carbohydrates, which makes sustainability weak.
Depending on the type of fats eaten, lipid profile can take a hit. Although keto diets generally tend to improve TG and HDL, many experience an increase in LDL, the bad cholesterol.
Ketoacidosis is another risk factor which increases when the production of ketones ramps up. It can lead to increased calcium excretion affecting bone mineral density loss, and also elevated uric acid and kidney stone risk.
Hormonal imbalances are also a common trait. Particularly in women, a ketogenic diet can disrupt menstrual cycle and lead to low thyroid hormones which disrupt both energy and reproductive health.
Are there any negative side effects to the keto diet?
Negative side effects of the keto diet can include the “keto flu” (headaches, fatigue, and irritability), nutrient deficiencies, digestive issues, and potential long-term cardiovascular risks if unhealthy fats are consumed.
Who should avoid keto diet?
People with certain medical conditions like liver disease, pancreatic insufficiency, or eating disorders, as well as pregnant or breastfeeding women, should avoid the keto diet unless advised by a healthcare provider.
Thyroid Hormones and Metabolic Rate
Thyroid hormones regulate metabolism. TSH activates the thyroid gland to produce T3 and T4, hormones crucial for energy metabolism, temperature regulation, metabolic function, and bone health. (40)
Increased carbohydrate intake leads to increased T3 production, suggesting an increase in metabolic rate. Calorie restriction lowers thyroid hormones, suggesting a decrease in metabolic rate. Generally, higher thyroid hormone levels represent faster metabolism that most associate with fat loss.
During ketogenic eating, LCHF or fasting, there’s a drop in T3 thyroid hormone, while T4 are elevated or stay the same. This effect isn’t directly associated to a decline in fat loss. In fact, data shows reduction in insulin and fat mass with carb restriction. (41) (42)
The reduction in T3 levels doesn’t reduce the ability to lose fat. T3 secretion is stimulated via elevations in glucose and insulin. During glucose starvation the need for T3 is reduced as the metabolism becomes more efficient, due to the use of ketones. Ketogenic diets maintain metabolic rate through other mechanisms like increased fat oxidation and ketone utilization.
The body just adapts to a lower metabolic demand, oftentimes confused with hypothyroidism. While ketosis reduces T3 levels, it doesn’t trigger a compensatory rise in TSH, meaning the body interprets this as adaptive state, not a deficient one. Despite a lower T3, ketogenic diets may still preserve energy expenditure due to a higher thermogenic effect.
Does keto affect thyroid levels?
Keto diets may cause a minor reduction in T3 hormone, signalling a light reduction in metabolic rate. However, this isn’t linked to impaired fat loss, may not occur in everyone, and TSH and T4 levels are still stable.
Does thyroid affect metabolic rate?
Yes, thyroid dictates metabolic rate. Higher levels of thyroid hormones, particularly T3 signals higher energy expenditure, or a faster metabolism. Carbohydrates play a role in converting T4 to the active T3 hormone.
Does keto increase metabolic rate?
No. If measured by T3 levels, keto diets may even reduce metabolic rate. However, ketogenic diets may still preserve energy expenditure due to a higher thermogenic effect and breakdown of fat.
