Macros, or macronutrients, provide the body with energy. Several diets are based on the restriction or promotion of certain macronutrients. With foods being comprised of the three macronutrients (protein, carbohydrate, and fat) and dietary fiber, make up the foods people eat. Different foods contain different amounts of these macronutrients. By modifying the amounts of one or more of these in the diet will have an impact on food choices. Protein, fat, and carbohydrates each contain a different amount of energy per gram (g).
The manipulation of macronutrient content in isocaloric diets has been studied to determine which composition best promotes weight loss while including other metabolic benefits. Increased protein and decreased carbohydrates are the most common modifications and have resulted in several popular diets created over time.
Changes in the macronutrient composition affect hormones, metabolic pathways, gene expression, and the composition and function of the gut microbiome that might effect fat storage.
Metabolically, carbohydrates elevate insulin secretion, thereby directing fat toward storage in adipose tissue, described as the carbohydrateinsulin model of obesity. In this context, low-carbohydrate diet [LCDs] ranging from 20 to 120 g of carbohydrates claim to treat obesity because they promote reduced insulin secretion and increased glucagon, which cause a metabolic shift to higher fat oxidation. LCDs can be designed to be either normal-fatHP or high-fat [HF]normal-protein.
However, despite the theory of the carbohydrateinsulin model, clinical trials comparing LCDs with low-fat diets (LFDs) in isoprotein diets reported similar weight loss and even higher body fat loss when reducing fat but not carbohydrates. Moreover, an important meta-analysis concluded that energy expenditure and fat loss were more significant with LFDs when compared with isocaloric LCDs.
Another type of very low carbohydrate (LC) high fat (HF) diet, known as the ketogenic diet(KD), prescribes a minimum of 70% of energy from fat and a severe restriction of carbohydrates to mimic a fasting state and induce ketosis
Finally, high-protein diets (HPDs), in which 20% of energy is derived from protein, appear to offer advantages regarding weight loss and body composition in the short term. Popular HP- HF diets, such as Atkins or Zone, promoted significant weight loss for short periods. Moreover, HP-HF diets are often associated with a high intake of animal products and saturated fat, causing detrimental effects of increased low-density lipoprotein cholesterol.
Manipulation of macronutrient content
Low-fat, High-fat, High-protein, Low-carb
Short-term: high-protein- low-carb (HP-LC) diets might present benefits HP-LC prescribed as jump start with caution (adverse effects)
Long-term: different ratio of macronutrients promotes similar weight loss (when associated with caloric
Low-Energy Diets (Low-Calorie Diets) Low-energy diets have a low number of total calories, about 800 - 1,200 kilocalories per day (kcal/d). Those less than 800 kcal/d are known as very low-energy diets.
Low-energy diets (LED) are those that contain a low amount of total calories. Typically, low-energy diets will be of about 800 to 1,200 kilocalories per day (kcal/d). Those less than 800 kcal/d would be classed as very-low-energy diets (VLED). The obvious advantage of utilizing an LED or VLED is that weight loss will occur at a much faster rate than other diets. Therefore, such diets may be particularly useful in situations where rapid weight loss can have profound health benefits (e.g., in obese patients).
ADVANTAGES
Rapid weight loss
Useful for overweight/obese populations
May improve health markers
DISADVANTAGES
Increased risk of muscle loss
Decreased athletic performance
Increased risk for micronutrient deficiencies
Increased hunger and difficult adherence
Low-Fat Diets (LFD)
A diet with fat intake around 20-35% of total calories.
While there is no exact definition of a low-fat diet (LFD), it typically describes a diet where fat intake is 20 to 35% of total calories. The advice to decrease dietary fat intake to 20 to 35% of total calories has been given for many decades at a public health level. Diets below that lower cut-off of 20% of total calories are often referred to as very low-fat diets (VLFD).
ADVANTAGES
Reduced body weight and body fat
Improved health markers
DISADVANTAGES
Limits food choices
May decrease certain sex hormones
Potentially difficult adherence
Low-Carbohydrate (LC) Diets A diet where carbohydrate content is 40% or less of total calories.
Similar to low-fat diets, there is no agreed on definition of a low-carbohydrate diet with its classification varying wildly from study to study. Studies typically classify a diet as low-carbohydrate if the carbohydrate content is 40% or less of total calories. However, many have argued that for a diet to be defined as truly low-carbohydrate, then the carbohydrate intake should be much lower, e.g., 50 to 150 g/d or < 20% of total calories.
ADVANTAGES
Reduced body weight and body fat
Improved health markers
Avoidance of hyperpalatable (sugary) foods
DISADVANTAGES
Suboptimal diet for certain athletes
Potential for increased cholesterol consumption
Potentially difficult adherence
Ketogenic Diets
A diet where carbohydrate content is less than 5% of total calories, protein intake is moderate (20-30%) and fat intake is high (65-75%).
The ketogenic diet has been around since the 1920s as a diet plan to reduce seizures for patients with epilepsy. It involves consuming a large percentage of calories from fat, moderate percentage of protein, and very little carbohydrate. It is a combination that leads to the physiological state of (nutritional) ketosis. Ketosis is a natural metabolic state that occurs when the body starts producing ketones (ketone bodies) from fat. The body can use these ketones as a fuel (substrate) source to generate energy in place of glucose (which is now scarce).
ADVANTAGES
Effective for patients with epilepsy
Weight loss
Improved health markers
Avoidance of hyperpalatable (sugary) foods
DISADVANTAGES
Potential for increased LDL cholesterol
Potential nausea and vomiting at initiation of diet
Potential fatigue and headaches at initiation of diet
Potentially difficult
High-Protein Diet A diet containing more than 25% of total calories from protein.
A high-protein diet is typically defined as one containing more than 25% of total calories from protein or above 1.2 grams of protein per kilogram of body weight (g/kg) or 0.54 g/lb. The recommended daily allowance (RDA) for protein is currently set at 0.8 g/kg (0.36 g/lb). However, there is strong evidence showing multiple health and body composition benefits to consuming higher amounts, especially in the range of 1.2 to 1.6 g/kg (0.54 to 0.73 g/lb).
ADVANTAGES
Weight loss
Improved health markers
Muscle gain when combined with resistance training
DISADVANTAGES
Potentially dangerous for people with existing kidney disorders
May restrict fiber intake if fiber-rich foods are not consumed
Potentially difficult adherence
Final remarks and conclusion
In conclusion, macronutrients [proteins, fats, and carbs] play essential roles in major bodily functions. In the short term, HP-LCDs are suggested to present benefits for weight-loss. However, owing to their major effects on metabolism and gut health, they should be considered as a jump-start weight loss tool rather than a diet for life. In the long term, current evidence indicates that a different ratio of macronutrients associated with a caloric restriction in healthy diets promotes similar weight loss
Keeping track of a person’s macro intake may help some people reach their health and fitness goals. However, for others, counting macros is time-consuming and restrictive. While there are benefits to counting macros, there are also risks. It is advisable to talk with a healthcare provider or a nutritionist before starting a macro diet.
The creation of new diets will continue to follow popular trends. However, the belief that these diets promote weight loss has emerged more from personal impressions and reports published in books, rather than from rigorously controlled research. Over the past several decades, efforts have been concentrated on clinical trials to determine the best diet for the treatment of obesity. Unfortunately, the evidence remains inconclusive and con-tested, and the trials present important limitations.
In the short term, diets promote different degrees of success, but in the long term, the small differences do not instill confidence for prescribing one diet over another. The number of unanswered questions remains large.
Why do some individuals experience successful weight loss, whereas others are more resistant to losing weight?
How do different diets change hormonal secretion, gut microbiome composition, and gene expression?
How do these changes regulate appetite and energy expenditure?
In the future, further investigation into these factors (such as hormone profiles, gut microbiome composition, and genetics/epigenetics) might allow us to indicate the most successful diet for each individual.
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