How to lose weight healthily, according to science


Should I count calories?

Counting calories helps build awareness of our energy consumption and can help monitor the energy deficit needed to lose weight. But food is more than calories. Reducing it to a number oversimplifies its nourishment.

Not all calories are nutritionally equal. Also, the body metabolises foods differently; it may absorb more calories from a corn tortilla than from an equivalent amount of sweetcorn.

Calorie counting can lead to restrictive behaviours or unhealthy habits. It is tempting to eat highly processed foods because calories are displayed on packaging and easier to count, or to exclude nutrient-dense foods like oily fish and nuts on the basis of their calories.

Many people monitor the calories they burn in exercise by using a fitness tracker, but one study found that these can overestimate the calories burned while walking by more than 50 per cent. Relying strictly on these tools, rather than to gauge broadly energy intake and expenditure, may encourage compulsive logging and result in overconsumption.

If you choose to count, do it within a healthy, balanced diet – and listen to your body’s hunger cues.

Counting calories can lead to unhealthy restricting behaviours (Photo: Martin Barraud/Getty)

Should I cut or reduce carbs?

Low-carb diets, like Keto, Atkins, and Dukan, advocate the elimination or marked reduction of carbohydrates such as grains (pasta, rice, and breads), starchy fruits and vegetables, and legumes. This is popularly seen as the big secret to weight loss – but simply isn’t true.

Everyone’s carbohydrate needs vary depending on age, sex, build, and activity levels. If you feel you consume more carbs than is right for your body, reducing to bring balance to your diet is sensible. That’s not the same as going low-carb.

Carbs are often dismissed as fattening. It is true that society’s carbohydrate requirements have reduced due to less active lifestyles, yet carbs remain important in a balanced diet. Japan has one of the lowest obesity rates and one of the highest rates of carbohydrate consumption.

Energy from carbs (in the form of glucose) can be converted to glycogen molecules and stored along with the water needed to reconvert it to glucose for future use. On a low-carb diet, the body makes fewer glycogen stores, so the corresponding water is absent. This sudden weight loss is often confused for fat loss.

Studies show there is no significant difference in weight loss between low-carb and low-fat diets. While research reveals a reduction in weight on the ketogenic diet, it is not sustained long term. These studies have a high dropout rate, showing just how difficult it is to stick to a low-carb diet.

Low carb diets often exclude many nutritious fruit and vegetables (Photo: Sean Gallup/Getty)

Carbs offer many health benefits. Suddenly restricting them can lead to headaches and digestive symptoms. The fibre in carbs improves digestion and maintains steady blood sugar levels. The keto diet, which excludes many fruits and vegetables, may cause constipation, and ketogenic dieters can miss out on the long-term health benefits of nourishing their gut bacteria.

Restricting carbs can cause fatigue, low mood, and food cravings. It is not recommended for those recovering from an eating disorder or disordered eating, or for children.

Restricting any food group can result in nutritional deficiency. When carbs are removed or restricted, we may turn to other macronutrients to plug the gap. Dietary proteins and fats may increase to unhealthy levels, which can reduce feelings of hunger to help with weight loss, but cause other issues such as increased cholesterol.

Research found young healthy adults following a low-carb, high-fat diet had a 44 per cent increase in LDL cholesterol (the “bad” type). Keto diets encourage foods high in fat, but if you don’t differentiate between saturated and unsaturated fats, your LDL levels could easily increase, raising heart disease and stroke risks.

Intermittent fasting has become popular but eating breakfast in particular can help weight loss (Photo: Wachara Kireewong/EyeEm/Getty)

Is it OK to skip meals?

There are three main types of intermittent fasting (IF):
■ Whole-day fasting: this includes the well-known 5:2 diet, with a limited 400–500 calorie intake on two days of the week only.
■ Alternate-day fasting: on fasted days it’s recommended you eat just one meal.
■ Time-restricted eating: an example is the 16:8 plan, where you eat the same amount of food as usual, but during an eight-hour window each day. Often, followers opt to skip breakfast.

These diets are popular because they offer a straightforward way to reduce energy intake that often leads to weight loss. Many people following time-restricted eating “fast” while asleep, then eat fewer calories than normal because they have a shorter time period within which to eat.

However, IF won’t work for everyone. The restrictions can potentially lead to overeating, bingeing, or even eating disorders.

Be careful of skipping any meals, but breakfast appears to be especially important when maintaining a healthy weight. Research suggests that controlling food intake across the day is more manageable on a full stomach in the morning – people who eat breakfast appear more likely to maintain weight loss in the long term. If you are considering any type of IF, breakfast may not be your best choice of meal to miss.

Liquid diets can be convenient, but there are downsides (Photo: Julia Murray/EyeEm/Getty)

Can liquid foods help me lose weight?

Meal replacement shakes and soups are often hailed as rapid weight-loss methods, and liquid meals can help as kick-starters. But research suggests they are effective only in the short-term. They are not recommended for long-term use – and the potentially tricky return to solid foods increases the chance of weight gain.

Research into liquid meals shows some positives. Participants who restricted their oral intake to 800 calories per day on a liquid diet achieved significant weight loss at 12 months. They had foods reintroduced after three to five months and managed to maintain weight loss, because these regimes can help people realise that they can lose weight and experience positive benefits to their physical and mental wellbeing, instigating behaviour change.

Meal-replacement products can also be convenient for busy dieters, eliminate decision-making at meal times, and are often fortified with micronutrients.

But there are cons too. Chewing enhances nutrient absorption. One study found that chewing almonds between 25 and 40 times suppressed hunger and increased the body’s ability to absorb nutrients from the almonds. Those who don’t chew properly can experience digestive problems and end up snacking more later. The same is true for those relying on liquid meals.

Problems can arise when individuals return to regular meals. It is easy to slip into old habits and regain the weight. This can be amplified by hormonal changes in the body following dietary restriction and a lowered metabolic rate. Liquid meals can instil a poor relationship with food.

In addition, following a set diet plan can reduce an individual’s ability to respond to internal hunger cues and skew feelings of satiety – making the transition back to solid food even harder. Lastly, liquid meals take away the enjoyment of eating meals with family and friends, a significant contribution to wellbeing.

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There is nothing wrong with liquid foods alongside a balanced diet of solids. Make soups with lots of vegetables to add plenty of fibre into your diet, and the odd smoothie is an easy way to get lots of nutrients into your diet, especially if you don’t enjoy fruits and vegetables.

Can my gut bacteria help me lose weight?

Research suggests that the gut microbiota – the trillions of bacteria that reside in our gut – may be an influential factor in our ability to lose weight. We know that gut bacteria are also involved in immunity, hunger and digestion – and no two people have the same composition.

One study, which placed 26 participants on a low-calorie diet rich in fruit and veg, found that some people lost more weight than others. Analysis showed this was probably due to a difference in their gut bacteria, which could influence how efficiently food was broken down and thus how much weight was lost.

In another study, researchers analysed the gut bacteria of 169 obese and 123 non-obese adults and found that 23 per cent of those who had lower diversity of bacteria were more likely to be obese.

These differences are probably due to a combination of genetics and environment. But we can increase our gut microbiota diversity by consuming a varied, mainly plant-based diet that is rich in fibre, and trying probiotic fermented foods.

Losing weight: what works for most people

  • Eat a healthy, balanced diet
  • Practise portion control
  • Eat less-healthy foods that you enjoy, only occasionally
  • Listen to your body: eat when you’re hungry and stop when you’re full
  • Exercise regularly, ideally 30 minutes daily
  • Try some strategies to manage stress; it increases the hormone cortisol, which lowers blood sugar and increases food cravings
  • Get enough sleep; this will help to control cortisol

If diets don’t work, what does?

“Dieting” is often unsustainable, with one analysis of 14 popular programmes finding that weight loss was mostly reversed after 12 months. By understanding how the concept affects our thinking, we can identify more effective approaches.

As babies, we are in tune with our body’s hunger signals and only eat what we need, but as we age we are surrounded by messaging and social pressures around food and lose this innate ability. The complex psychology surrounding our relationship with food undoubtedly plays a role in the failure of diets and can be the biggest barrier to weight loss.

Research shows that restrained eaters experience more intense food cravings, heightened emotions surrounding food, and greater preoccupation with it. Likewise, categorising foods as “good” or “bad” creates a restrictive mindset that increases cravings and the risk of overeating these foods when they are available.

Labelling foods as treats implies they can only be eaten once earned, which increases desire. Goal setting can also have detrimental psychological effects, as veering “off plan” can prompt feelings of failure and guilt, and subsequent overeating.

Slow, steady weight loss over a longer time period is the most effective way to lose body fat. According to one study, sustained adherence to a diet – rather than following a certain type of diet – is the key to successful weight management.

Instead of cutting out entire meals and risking fatigue and cravings, aim to control your meal sizes and choose healthier snacks. Eating more variety is also thought to enhance weight loss; try different types of meals and vegetables each day.
© Rhitrition Limited

This is an edited excerpt from ‘The Science of Nutrition: Debunk the Diet Myths and Learn How to Eat Responsibly for Health and Happiness’ by Rhiannon Lambert (Dorling Kindersley, £20)



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