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In this article, we describe the scientific evidence from research for the efficacy and safety of various weight-loss tips like:
Low-calorie diet (LCD) and very low-calorie diet (VLCD)
Very low-calorie ketogenic diet (VLCKD)
Meal replacements (MR)
Non-caloric sweeteners (NCS)
Role of proteins
Role of fiber
Role of water
Intermittent fasting (IF)
Time-restricted feeding (TRF)
Mediterranean diet
Micronutrients (capsaicin, caffeine, polyphenols, Vitamin D, resveratrol, alpha-lipoic acid, carnitine, and chromium)
Herbal weight loss preparations
Physical exercise
Cognitive-behavioral therapy
Obesity (or being excessively overweight) is characterized as having a Body Mass Index equal to or more than 30 kg/m2. Obesity is a result of net calorie excess in the body, which gets stored in the fatty tissue. Many factors may play a role in the development of obesity. The most common ones are overeating and physical inactivity. Other factors like genetics and metabolism may also play a role.
It is generally perceived that overweight people are less attractive. This has made people conscious of their appearance, as a result of which many have resorted to various lifestyle modifications like dieting and exercise for losing weight. Although this is a welcome move, it is also important to know that the real harm of obesity lies in its impact on health.
In obesity, there is chronic low-grade inflammation, especially in the fatty tissue. In the long run, excess body weight is a risk factor for several diseases like high blood pressure (called hypertension), high blood glucose (called diabetes), and heart attacks and brain strokes (due to atherosclerosis). Obesity has also been linked to the development of certain cancers. Recently, obesity has been identified as a risk factor for developing a severe form of coronavirus disease (COVID- 19). Hence, it is important to lose weight to not only look good but to stay fit and healthy.
Weight loss can be achieved in many ways. The best way to lose weight naturally is the modification of diet to restrict the total daily intake of calories. Including physical exercise (like aerobics or resistance training) in the daily routine is another effective intervention and can complement energy restriction. An often overlooked concept to reduce weight is the cognitive behavioral therapy, which can add to the above two. Below, we will discuss, citing all the available scientific evidence, these different approaches to weight loss.
Dietary tips for weight loss
Diet is the sum of food consumed by a person. It includes macronutrients and micronutrients. Macronutrients are of three types, namely carbohydrates, proteins, and fats. Total macronutrient quantity contributes to the daily calorie intake and it can be reduced for weight loss.
These macronutrients can be taken in standard proportions as recommended by professional organizations, or in modified proportions for weight loss. An example of a weight loss diet, where the macronutrient proportion is modified, is the very low-calorie ketogenic diet (VLCKD), commonly called the ‘keto diet’, in which the daily carbohydrates intake is restricted to less than 10%. Carbohydrate intake can also be reduced by replacing table sugar with non-caloric sweeteners (NCS). Increasing intake of some nutrients like protein and fiber can also promote weight loss.
Another approach to weight loss is modifying the dietary pattern of eating. Examples of these include intermittent fasting (IF) and time-restricted feeding (TRF).
Finally, some micronutrients can be useful for weight loss. These micronutrients may promote weight loss by various mechanisms like increasing the metabolism, inhibiting the absorption of macronutrients, etc.
What is the ideal daily calorie intake and proportion of macronutrients (like carbohydrates, protein, and fats) in the diet?
Total daily calorie need depends on factors like age, sex, and the level of physical activity. Estimates for total daily energy intake range from 1,600 to 2,400 calories per day for adult women and 2,000 to 3,000 calories per day for adult men. See U.S. Department of Health and Human Services for further details.
Apart from various specialized roles of these individual macronutrients, the role common to all three is the provision of energy for the normal functioning of the body. One gram of carbohydrate, fat, and protein provide four, nine, and four calories, respectively.
On the surface, it may seem wise to avoid fats for weight loss. However, this is not advisable as fats too have important functions other than providing energy; an ideal diet plan should have a holistic approach to health and not just weight loss. This is why professional organizations have given recommendations for the ideal proportion of these macronutrients. For example, the US Department of Health and Human Services and US Department of Agriculture recommend 45-65% calories of daily diet from carbohydrates, 25-35% from fats, and 10-30% from proteins, with added sugars and saturated fats contributing less than 10% of daily calories.
Low-Calorie Diet (LCD) and Very Low-Calorie Diets (VLCD) may be effective for the short term management of weight loss but may cause loss of lean body mass (LBM)
Low-calorie diet and very low-calorie diet involve consuming 800 to 1200 calories and 400 to 800 calories per day, respectively [Aragon and colleagues, 2017].
The aim is to create a net calorie deficit to lose weight. These diets can be implemented by various strategies like decreasing the portion size of meals, having lower-calorie foods like vegetables instead of energy-dense foods, skipping some meals of the day altogether, etc.
Calorie restriction may not only be useful for weight reduction but may have an added advantage of reducing inflammation in the body.
Although these diets can induce rapid weight loss, it may be difficult to adhere to these diets. Hence, these diets may not be effective for weight maintenance following weight loss.
Another side effect of these diets is the loss of lean body mass (LBM) [Willoughby and colleagues, 2018]. Lean body mass is primarily due to skeletal muscle, but also due to organs, bones, body water content, etc. Loss of lean mass is not desirable, as it may have unfavorable consequences like reduced functionality of the individual.
Very Low-Calorie Ketogenic Diet (VLCKD) may be effective but some studies have shown that death rates are higher for keto diet
A low carbohydrate diet is defined as one in which the daily total energy intake (TEI) from carbohydrates is less than 45%. An extreme form of low carbohydrate diet is the very low-calorie ketogenic diet (VLCKD), in which the daily energy contribution of carbohydrates is less than 10% (carbohydrates less than 50 g/day) [Accurso and colleagues, 2008].
It is a well-known fact that ketogenic diets are effective for weight loss [Gershuni and colleagues, 2018]. However, some studies like the one by Kwon and colleagues, 2020 have shown that diets with high (>60%) or low (<50%) proportions of calories from carbohydrates are linked to an increased rate of deaths.
Meal replacements (MR) may not be effective for the long term management of weight loss
Another way to reduce calorie intake in the diet is by consuming meal replacements (MR). In meal replacement, at least one meal of the day is replaced by food, food products, drinks in the form of soups or shakes, bars, or ready-to-consume (pre-packaged) meals. Other meals of the day can be consumed as usual. Meal replacements are usually a part of commercial weight-loss programs but can also be purchased over the counter.
When all the meals of the day are replaced, it is called total diet replacement (TDR). TDR contains specially formulated meals intended to be the only source of nutrition and hence have to be consumed under medical supervision.
Usually, commercial weight-loss programs also provide some form of support (either in person or over the phone) like dietary advice, motivational interviewing, etc.
Meal replacements may be useful for rapid weight loss but the efficacy of meal replacements to sustain weight loss for long periods may be questionable. This is because it may be difficult to adhere to meal replacements for prolonged periods and make it a part of daily life. This is probably the reason why meal replacements do not form a part of official recommendations for the management of overweight and obesity in many countries like the USA, Singapore, and Australia. See Astbury and colleagues, 2019 for further details on meal replacements.
Substituting added sugar with non-caloric sweeteners (NCS) can be effective for losing weight
Another effective intervention for weight loss is the exclusion of ‘free’ or ‘added’ sugars in the diet. Sugar can be replaced by non-caloric sweeteners (NCS) like acesulfame-K, aspartame, steviol glycosides, saccharin, and sucralose. Again, it is also important to note that excessive consumption of these non-caloric sweeteners can cause side effects, and they should be consumed only within acceptable and safe daily intake limits [Cavagnari and colleagues, 2019].
Higher protein consumption is essential for any weight loss intervention
During any weight loss intervention, loss of body weight can occur not only by the loss of fat but by the loss of lean body mass (LBM, also known as ‘fat-free mass’). It is estimated that approximately 25% of weight loss in overweight individuals during any weight loss intervention involving calorie restriction may be due to loss of lean body mass [Weinheimer and colleagues, 2010]. In normal-weight individuals, the contribution of lean body mass (LBM) loss to total weight loss maybe even higher. One of the most effective ways to preserve the lean body mass during any weight loss intervention is increasing the protein intake in the diet.
Increased protein intake during any weight loss intervention not only preserves the lean body mass but also results in higher fat loss. This is because the thermic effect of food (TEF) is highest in proteins (20-30%) compared to carbohydrates (5-10%) and fats (0-5%). The thermic effect of food is the number of calories required to digest, absorb, metabolize, and store the food. This is why, in both the low carbohydrate and fat diet, it is best to compensate the calories from carbohydrates or fats with protein.
During energy restriction, it is recommended to have equal to or more than 1 g/kg/day of protein instead of the recommended 0.8 g/kg/day for states of energy balance [Kim and colleagues, 2016]. Having said the above, too high protein intake (usually above 2 g/kg/day) can put an extra burden on the kidneys, bones, and liver; they can even increase the risk of heart disease (coronary artery disease) and cancer [Delimaris and colleagues, 2013].
Having adequate fiber in the diet can help lose weight
Fiber promotes weight loss by numerous mechanisms (which are not discussed here).
It is estimated that only 5% of the population has an adequate daily intake of fiber. American Dietetic Association recommends 25 grams/day for adult women and 38 grams/day for adult men.
Foods high in fiber are fruits, vegetables, legumes (lentils, beans, and peas), whole grains, nuts, and seeds. Fiber can also be consumed in the form of psyllium husk supplements. See Slavin and colleagues, 2013 for further details.
Increasing water consumption may be helpful for weight loss
Many people do not consume an adequate amount of water during the day. Studies have shown that increasing liquid consumption (uniformly throughout the day or before meals) can help in weight reduction [Castello and colleagues, 2019]. Recommended upper limits of daily fluid consumption for adult men and women are 3.7 liters and 2.7 liters, respectively [Popkin and colleagues, 2010].
Water consumption is usually higher in conditions like hot weather. However, consuming too much water under normal conditions can lead to serious complications like lower sodium levels in the blood (hyponatremia), which can even result in death.
Intermittent fasting (IMF) may produce similar results when compared to continuous energy restriction (CER)
As discussed earlier, calorie (energy) restriction is the cornerstone of any weight loss intervention. Current guidelines recommend the conventional continuous energy restriction (CER), which is a daily restriction of 30% (or 500 to 750 calories) from baseline requirements, for the treatment of obesity [Maclean and colleagues, 2015]. However, newer strategies like intermittent fasting (IMF) have been touted to be better alternatives for weight loss than continuous energy restriction. Intermittent fasting is an eating pattern in which individuals have periods of little (that is, 25-40 % of daily energy requirements) or no energy intake. These periods last from 16 to 48 hours. These periods of fasting alternate with periods of normal food intake. The two most widely used strategies of intermittent fasting are the 5:2 intermittent fasting (that is, two ‘consecutive’ or ‘nonconsecutive’ fast days in a week) and alternate day intermittent fasting (ADF). However, studies comparing intermittent fasting to continuous energy restriction have shown that none of these strategies is superior to the other for weight loss. See Ciofi and colleagues, 2018 and Rynders and colleagues, 2019 for further details.
Time-restricted feeding (TRF) can be effective for losing weight
Time-restricted feeding (TRF) is a strategy when food consumption is usually restricted to 8 to 10 hours during the daytime on most days of the week. Time-restricted feeding is a specific feeding pattern and is not necessarily concerned with energy (calorie) restriction. Animal studies (on rodents) have shown that time-restricted feeding is effective in improving metabolism and reducing weight. In humans, the data is scarce, but preliminary evidence favors a positive impact of time-restricted feeding for weight loss [Rynders and colleagues, 2019].
Mediterranean diet may be effective for weight loss
Interestingly, a Mediterranean diet was found to be more effective than low-fat diet for weight loss [Shai and colleagues, 2008].
The traditional Mediterranean diet comprises of a high proportion of vegetables, fruits, legumes (like lentils, beans, and peas), unprocessed (whole grain) cereals, and nuts. It has a low proportion of dairy and meat, and a moderate proportion of fish. The fat proportion may be moderate or high, but mainly in the form of mono-unsaturated fats from olive oil [Trichopoulou and colleagues, 2015].
Certain micronutrients (capsaicin, caffeine, polyphenols, Vitamin D, resveratrol, alpha-lipoic acid, carnitine, and chromium) have shown to promote weight loss
Micronutrients are nutrients present in minute quantities in foods. They may boost metabolism and help burn fat. Foods containing these micronutrients should be included in a weight loss diet. These micronutrients, which are usually present naturally in certain foods, are also available as supplements.
Scientific evidence for weight loss is available for the following micronutrients:
- Capsaicin (found in chili pepper) [Varghese and colleagues, 2017]
- Caffeine (present in coffee and tea) [Tabrizi and colleagues, 2019]
- Polyphenols (a group of plant bioactive compounds) in tea [Pan and colleagues, 2016]
- Vitamin D may not only be useful for weight loss [Perna and colleagues, 2019] but in preserving lean body mass [Beaudart and colleagues, 2014].
- Resveratrol (a plant bioactive compound most commonly found in grapes) [Tabrizi and colleagues, 2020]
- Alpha-lipoic acid (found in many food sources) [Kucukgoncu and colleagues, 2017]
- Carnitine (found in large quantities in animal meat) [Pooyandjoo and colleagues, 2016]
- Chromium (a trace element found in many foods) may not only be useful for weight loss but in preserving lean muscle mass [Willoughby and colleagues, 2018]
Certain herbal preparations may not only be ineffective but may cause serious complications
Contrary to popular belief, there is insufficient evidence to show that certain herbal preparations like Garcinia cambogia, Camellia sinensis, Hoodia gordonii, Citrus aurantium, and Coleus forskohlii may be helpful in weight loss. Moreover, they can occasionally cause serious complications and even death [Farrington and colleagues, 2019].
Before we conclude, let’s touch briefly on the role of physical exercise and cognitive behavioral therapy for weight loss.
Physical exercise can not only help lose weight but preserve lean body (muscle) mass
It is already discussed earlier how calorie restriction can unwantedly contribute to a loss of lean body mass and increasing dietary protein intake is one strategy to preserve it. Another effective strategy for the preservation of lean muscle mass is the inclusion of physical exercise (aerobics and/or resistance training) in the weight loss regime.
Similar to increasing protein intake, it is helpful in augmenting the effect of diet modification for weight loss [Villareal and colleagues, 2011]. This is because physical exercise increases the net energy expenditure. However, too much exercise can have adverse effects on health.
Cognitive-behavioral therapy for weight loss (CBTWL) can be a useful psychological intervention
Cognitive-behavioral therapy for weight loss (CBTWL) can help in weight loss by modifying eating behaviors like increasing cognitive restraint and reducing emotional/binge eating [Jacob and colleagues, 2018].
To conclude, weight loss can be best achieved by a combination of diet modification, physical exercise (cardio and/or weight training), and psychological interventions (like behavioral therapy). Some strategies may induce rapid weight loss but may be difficult for weight maintenance following weight loss. Weight loss may not only be due to fat loss but due to muscle loss. Finally, to preserve muscle mass it is important to have increased protein intake and do physical exercise.
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Cognitive Behavioral Therapy for Weight Loss