The world of weight loss is filled with various dietary approaches, each claiming to be the most effective. Among the popular options are the ketogenic diet (keto) and calorie deficit. This article aims to explore both approaches, examining their principles, potential benefits, and drawbacks, to help you make an informed decision about which might be suitable for you.
Understanding the Ketogenic Diet
The ketogenic (keto) diet is a high-fat, very low-carbohydrate diet. The keto diet is all about cutting carbs and eating more fat, similar to the Atkins diet from the 1970s. Most of the body's cells prefer to use blood sugar (glucose) as their main source of energy. Normally, your body's primary energy source is glucose, which comes from the breakdown of carbohydrates. The keto diet reduces your total carb intake to less than 50 grams a day. This is the equivalent of a cup of white rice. The keto diet excludes carb-rich foods like grains, beans, fruits and starchy vegetables.
How Keto Works
The keto diet limits carbohydrates, forcing your body to burn fat for fuel instead. The keto diet forces your body to use a different type of fuel. Instead of providing your body with glucose from carbohydrates, the keto diet relies on the liver to break down stored fat into molecules called ketones. When these stores are full, they are converted into fat. In this state, your body breaks down fats into molecules called ketones. Ketones serve as an alternative fuel source. For most people to begin using stored fat as fuel, they need to limit daily carbohydrate intake to fewer than 20 to 50 grams depending on body size. (For comparison, a medium-sized banana has about 27 grams of carbs.) But this is a highly individualized process, and some people need a more restricted diet to begin producing enough ketones. A true ketogenic diet calls for up to 90% of your daily calories to come from fat. That is often hard for people to maintain.
Potential Benefits of Keto
- Weight Loss: Research has shown that people can achieve faster weight loss with a keto diet compared with a calorie-reduction diet. There has been anecdotal evidence of people losing weight on the ketogenic diet.
- Appetite Suppression: People also report feeling less hungry than on other types of restricted diets.
- Specific Medical Conditions: The keto diet helps reduce seizures in children with epilepsy. The keto diet is being studied for reducing symptoms for patients with progressive neurological disorders like Parkinson’s disease.
Potential Drawbacks of Keto
- Difficulty in Adherence: Because of the stringent food restrictions, many find the keto diet hard to stick to.
- Nutrient Deficiencies: Because the keto diet is so restricted, you’re not receiving the nutrients - vitamins, minerals, fibers - that you get from fresh fruits, legumes, vegetables and whole grains. People report feeling foggy, irritable, nauseous and tired. In particular, low fiber intake can disrupt gut microbiota and lead to chronic constipation, while inadequate magnesium, vitamin C and potassium can contribute to muscle cramps, fatigue and weakened immune function.
- Heart Health Concerns: The high-fat nature of the diet could also have negative impacts on heart health. The American Heart Association recommends limiting saturated fat intake to less than 6%. In practice, many people eat high amounts of saturated fats, which could increase your risk of heart disease. You may be eating a lot of fatty meat thinking it’s a good thing for you because it's high in fat. This can dramatically alter your lipid profile. While high-fat diets can elevate LDL (“bad”) cholesterol, the type of saturated fat matters. The bottom line is that having more fats in your diet can lead to higher cholesterol. We know that higher cholesterol tends to increase your chances of heart attacks and strokes.
- Kidney Issues: The keto diet may not be appropriate for everyone, specifically people with kidney disease. Although more research is needed in that area, there is some suggestion that it can make kidney disease worse over time.
- Dehydration: Some people also experience dehydration on the keto diet because they’re eliminating glycogen, which holds water, from the bloodstream.
- Disconnection from Intuitive Eating: When you micromanage your food intake by tracking how much you eat, it disconnects you from what your body is asking for. You start using outside numbers to determine what to eat instead of listening to your body. Monitoring food so closely can lead to psychological distress, such as shame and binge eating.
- Blood Pressure and Blood Sugar Drops: The keto diet can cause your blood pressure to drop in the short term due to a reduction in blood volume and changes in your fluid balance. Symptoms of low blood pressure include dizziness, lightheadedness or fainting, especially when standing up quickly. Following a keto diet can also cause your blood sugar to drop, which can be dangerous for people living with diabetes. Common symptoms of low blood sugar include weakness or shaking, sweating, a fast heartbeat and dizziness.
Understanding Calorie Deficit
The first law of thermodynamics dictates that body mass remains constant when caloric intake equals caloric expenditure. Obesity results from an excess of energy intake over energy expenditure. If the obese individual wants to lose weight, then the solution is extremely simple: energy expenditure must exceed energy intake for a suitable length of time.
How Calorie Deficit Works
To lose weight, you need to consume fewer calories than you burn. This forces your body to use stored energy (fat) to make up for the deficit, leading to weight loss.
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Potential Benefits of Calorie Deficit
- Flexibility: A calorie deficit doesn't restrict specific food groups, offering flexibility in food choices.
- Sustainability: It is easier to sustain long-term as it doesn't require drastic dietary changes.
- Overall Health: It can be tailored to meet individual nutritional needs and promote overall health.
Potential Drawbacks of Calorie Deficit
- Requires Tracking: It requires tracking calorie intake, which can be tedious for some.
- Slower Results: Weight loss may be slower compared to very restrictive diets like keto.
- Potential for Nutrient Deficiencies: If not planned carefully, it can lead to nutrient deficiencies.
DIETFITS Study: Low-Fat vs. Low-Carb Diets
A major new randomized clinical trial (RCT) on low-fat vs. low-carb diets provides valuable insights into weight loss. This year-long study, creatively named The Diet Intervention Examining The Factors Interacting with Treatment Success (DIETFITS), involved 600+ participants. It was conducted by Dr. Christopher Gardner of Stanford University in conjunction with the US National Institutes of Health (NIH), the Nutrition Science Initiative (NuSI), and a team of nutrition experts.
Study Design
This RCT assigned 609 participants to either a low-fat diet or a low-carb diet for 12 months. In total, 263 males and 346 premenopausal females free of major health conditions (i.e., no diabetes, cancer, heart disease, high cholesterol, etc.) were included in the study. Over the course of the study, each subject was instructed to attend 22 dietary counseling sessions with a registered dietitian; average attendance was 66% for both groups. During the first two months of the study, the low-fat group was instructed to consume only 20 g of fat per day and the low-carb group only 20 g of carbs per day. However, they were not expected to stay at these levels indefinitely: at the end of this 2-month period, they started adding fats or carbs back to their diet until they felt they’d reached the lowest intake level they could sustainably maintain. Neither group was able to stick to the very low starting intakes: by month 3, the low-fat group was already consuming an average of 42 g of fat per day, whereas the low-carb group was consuming an average of 96.6 g of carbs per day. It’s possible some in the low-carb group may have been in ketosis during these first two months due to the very low carb intake prescribed. While no caloric intake targets were given, both groups were instructed to consume high-quality whole foods and drinks. Specifically, they were instructed to “maximize vegetable intake … minimize intake of added sugars, refined flours, and trans fats; and … focus on whole foods that were minimally processed, nutrient dense, and prepared at home whenever possible.” A total of 12 random and unannounced multi-pass 24-hour dietary recalls were taken over the course of the study to assess food intake. With this method, an interviewer asks individuals to recall all the foods and drinks they have consumed in the previous 24-hours.
Study Hypotheses
This trial randomly assigned 609 participants to either a healthy low-fat diet or a healthy low-carb diet for 12 months. Over those 12 months, everyone was instructed to attend 22 dietary counseling sessions with a dietitian. The first primary hypothesis being tested was a potential link between genotype pattern and diet type for weight-loss success. All participants were screened for 15 genotypes, including 5 “low-fat” genotypes (hypothesized to do better on a low-fat diet), 9 “low-carb” genotypes (hypothesized to do better on a low-carb diet), and 1 “neutral” genotype. The second primary hypothesis being tested was a potential link between insulin secretion and diet type for weight-loss success. At the start of the trial and at months 3, 6, and 12, all participants completed an oral glucose tolerance test (OGTT) to measure insulin production. An OGTT is a test that can measure your blood glucose and/or insulin levels after you’ve consumed a fixed amount of carbohydrate (normally 75 g of glucose). Researchers looked to see if genotype or insulin production could predict weight loss on either a low-fat or a low-carb diet. Other health outcomes measured included weight change, body fat (DXA), cholesterol, blood pressure, and fasting glucose.
Study Results
While there were no significant dietary differences between groups at baseline (before the dietary interventions started), there were significant differences at months 3, 6, and 12 with regard to the percent intake of carbohydrate, fat, protein, fiber, and added sugars. Additionally, saturated fat intake was significantly reduced in the low-fat group, whereas the overall glycemic index was lower in the low-carb group. Additionally, within each group, differences in genotypes or insulin secretion made no significant difference in weight change. This suggests that neither the genotype tested for in this study nor the amount of insulin produced during the OGTT can predict weight-loss success on either a low-fat or a low-carb diet. Ironically, a potential confounding factor masking an interaction could have been that both diets were based on whole foods. Both groups were able to improve certain health markers (BMI, body fat percentage, waist circumference, blood pressure, and fasting insulin and glucose levels), although no significant differences were seen between groups. At the 12-month mark, low-density lipoprotein cholesterol (LDL-C) had significantly decreased in the low-fat group (-2.12 mg/dL), while it had increased in the low-carb group (+3.62 mg/dL). Resting energy expenditure (REE) was not significantly different between groups at any point. By month 12, REE had decreased significantly from baseline for both groups (-66.45 kcals for low-fat, -76.93 kcals for low-carb). Total energy expenditure (TEE) was not significantly different between groups or compared to baseline. No significant weight-loss differences were seen between the low-fat and low-carb groups, and neither genetics nor insulin production could predict weight-loss success on either diet.
Key Takeaways from DIETFITS
The program offered intensive dietary counseling and guidance for the entire length of the study. Many free-living trials provide instruction and/or support up front, after which the participants are left to their own devices. It confirmed the participants’ dietary intakes through random multi-pass 24-hour dietary recalls, bolstered by lipid panels and RER tests. It is one of the larger studies of its kind, which reduces the probability of a result being due to random error (aka “noise”). While our understanding of the interactions between genetics and diet are still growing, this trial has tested 15 genotype patterns suspected of being able to influence weight-loss success or failure on low-fat or low-carb diets. Even though no effect was seen, the authors have stated that they will analyze “all the genomic data obtained … Lastly, not every participant adhered perfectly to the assigned diet, which reduces our ability to draw a direct relationship between genotype, insulin production, and diet intervention. The DIETFITS study replicates the results of numerous other RCTs, showing that, when caloric intake and protein intake are both matched between diet interventions, the proportion of carbs or fat matters little for weight loss. Furthermore, genotypes and insulin production were not predictive of weight loss (but other genotypes and insulin markers have yet to be rigorously tested). One important aspect of this trial we need to consider, and one that is often overlooked, is interindividual variability. As you can see in Figure 2, weight changes differed drastically within both groups - ranging from 70 lbs lost (-32 kg) to 24 lbs gained (+11 kg). Each bar represents the weight change of a single participant. A second important aspect to consider is adherence. In the beginning of the study, all participants were instructed to consume either ≤20 g of fat (if in the low-fat group) or ≤20 g of carbs (if in the low-carb group) for the first two months, after which they could increase either their fat or carb intake to levels they felt they could sustain indefinitely. By the end of the trial, the vast majority had not been able to maintain such low levels. Real-life applicability matters greatly when extrapolating from a study’s results.
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The Importance of Diet Quality
Before worrying about the details, one should ensure their diet is more whole foods (with ample vegetables) than processed foods. The importance of diet quality was heavily emphasized in both study groups - something not traditionally given as much attention in other long-term diet trials. You can partially get this data from Table 2 in the paper: we report decreases in added sugar and glycemic load for both groups and a decrease in glycemic index for the low-carb group. We have also analyzed the entire study group, using the Healthy Eating Index score (HEI 2010). The diet assessment software does provide us with an overview of “whole grains” vs. We have a paper on this coming out, so I don’t want to give away the conclusion just yet!
Personalizing Satiety
We worked on personalizing satiety. The AHA/ACC/TOS guidelines for the management of overweightness and obesity in adults discuss two options for reducing energy intake (section 3.3.1): a “prescribed” caloric restriction, or an “achieved” caloric restriction. We did not “prescribe” a specific caloric restriction. We focused on reducing foods high in fats or foods high in carbs, and we advised the participants that they needed to find the lowest level of fat or carb intake they could achieve while not feeling hungry. We explained that if what they were doing left them feeling hungry, then when they achieved their weight-loss goal or the study ended, they would likely go off their diet and back to what they were eating before, and so the weight would likely come back on. We wanted for them to find a new eating pattern they could maintain maintain without even thinking of it as a “diet”. We got a lot of positive feedback from the participants: they were happy to not have to “count calories” (to not have to limit their daily caloric intake). Table 2 in the paper shows that the participants reported “achieving” a ≈500 calorie deficit, without us prescribing one … and it was fairly consistent through the 12 months. Now, I honestly think they likely exaggerated the caloric restriction. But in fact they did lose >6,500 lbs collectively by the end of the study (≈3,000 kg), even though the level of physical activity only went up a little in both groups (the level of activity they reached was not statistically different from baseline). So they must have eaten less.
Metabolic Considerations
The hormonal changes associated with a low-carbohydrate diet include a reduction in the circulating levels of insulin along with increased levels of glucagons, leading to activation of phosphoenolpyruvate carboxykinase, fructose 1,6-biphosphatase, and glucose 6-phosphatase and inhibition of pyruvate kinase, 6-phosphofructo-1-kinase, and hexokinase, favoring gluconeogenesis over glycolysis. Gluconeogenesis is an energy-consuming process as 6 mol of ATP are consumed for the synthesis of 1 mol of glucose from pyruvate or lactate. The transformation of gluconeogenic amino acids into glucose requires even more energy because ATP is needed to dispose of the nitrogen as urea. Also, a low-carbohydrate diet is often high in protein. A recent study demonstrated that postprandial thermogenesis was increased 100% on a high-protein/low-fat diet vs. a high-carbohydrate/low-fat diet in healthy subjects. Finally, ketogenic diets are characterized by elevations of free fatty acids, leading to the increased transcription of mitochondrial uncoupling proteins and of peroxisomal β-oxidation. Uncoupling proteins allow the proton gradient generated by the respiratory chain to re-enter the mitochondria by pathways which bypass the F1 ATPase, resulting in the generation of heat rather than ATP. Also, fatty acids undergoing β-oxidation with peroxisomes have no mechanism for energy conservation and result solely in heat production.
Is a Calorie Just a Calorie?
It is increasingly clear that the idea that "a calorie is a calorie" is misleading. The calorie content may not be as predictive of fat loss as is reduced carbohydrate consumption. Different diets (e.g., high-protein/low-carbohydrate vs. low-protein/high-carbohydrate) lead to different biochemical pathways (due to the hormonal and enzymatic changes) that are not equivalent when correctly compared through the laws of thermodynamics. Unless one measures heat and the biomolecules synthesized using ATP, it is inappropriate to assume that the only thing that counts in terms of food consumption and energy balance is the intake of dietary calories and weight storage. Recently, Feinman and Fine concluded: "Metabolic advantage with low carbohydrate diets is well established in the literature… Attacking the obesity epidemic will involve giving up many old ideas that have not been productive. "A calorie is a calorie" might be a good place to start." However, there will be metabolic accommodations and one cannot assume that the metabolic advantage (i.e., greater weight loss compared to isocaloric high-carbohydrate diet) will stay the same over a long term.
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