How much weight do you actually need to lose? It might be a lot less than you think

If you’re one of the one in three Australians whose New Year’s resolution involved losing weight, it’s likely you’re now contemplating what weight-loss goal you should actually be working towards.

But type “setting a weight loss goal” into any online search engine and you’ll likely be left with more questions than answers.

Sure, the many weight-loss apps and calculators available will make setting this goal seem easy. They’ll typically use a body mass index (BMI) calculator to confirm a “healthy” weight and provide a goal weight based on this range.

Your screen will fill with trim-looking influencers touting diets that will help you drop ten kilos in a month, or ads for diets, pills and exercise regimens promising to help you effortlessly and rapidly lose weight.

Most sales pitches will suggest you need to lose substantial amounts of weight to be healthy – making weight loss seem an impossible task. But the research shows you don’t need to lose a lot of weight to achieve health benefits.

Read more: Can you be overweight and healthy?

Using BMI to define our target weight is flawed

We’re a society fixated on numbers. So it’s no surprise we use measurements and equations to score our weight. The most popular is BMI, a measure of our body weight-to-height ratio.

BMI classifies bodies as underweight, normal (healthy) weight, overweight or obese and can be a useful tool for weight and health screening.

But it shouldn’t be used as the single measure of what it means to be a healthy weight when we set our weight-loss goals. This is because it:

• fails to consider two critical factors related to body weight and health – body fat percentage and distribution

• does not account for significant differences in body composition based on gender, ethnicity and age.

How does losing weight benefit our health?

Losing just 5–10% of our body weight – between 6 and 12kg for someone weighing 120kg – can significantly improve our health in four key ways.

1. Reducing cholesterol

Obesity increases the chances of having too much low-density lipoprotein (LDL) cholesterol – also known as bad cholesterol – because carrying excess weight changes how our bodies produce and manage lipoproteins and triglycerides, another fat molecule we use for energy.

Having too much bad cholesterol and high triglyceride levels is not good, narrowing our arteries and limiting blood flow, which increases the risk of heart disease, heart attack and stroke.

But research shows improvements in total cholesterol, LDL cholesterol and triglyceride levels are evident with just 5% weight loss.

2. Lowering blood pressure

Our blood pressure is considered high if it reads more than 140/90 on at least two occasions.

Excess weight is linked to high blood pressure in several ways, including changing how our sympathetic nervous system, blood vessels and hormones regulate our blood pressure.

Essentially, high blood pressure makes our heart and blood vessels work harder and less efficiently, damaging our arteries over time and increasing our risk of heart disease, heart attack and stroke.

Like the improvements in cholesterol, a 5% weight loss improves both systolic blood pressure (the first number in the reading) and diastolic blood pressure (the second number).

A meta-analysis of 25 trials on the influence of weight reduction on blood pressure also found every kilo of weight loss improved blood pressure by one point.

3. Reducing risk for type 2 diabetes

Excess body weight is the primary manageable risk factor for type 2 diabetes, particularly for people carrying a lot of visceral fat around the abdomen (belly fat).

Carrying this excess weight can cause fat cells to release pro-inflammatory chemicals that disrupt how our bodies regulate and use the insulin produced by our pancreas, leading to high blood sugar levels.

Read more: Can I actually target areas to lose fat, like my belly?

Type 2 diabetes can lead to serious medical conditions if it’s not carefully managed, including damaging our heart, blood vessels, major organs, eyes and nervous system.

Research shows just 7% weight loss reduces risk of developing type 2 diabetes by 58%.

4. Reducing joint pain and the risk of osteoarthritis

Carrying excess weight can cause our joints to become inflamed and damaged, making us more prone to osteoarthritis.

Observational studies show being overweight doubles a person’s risk of developing osteoarthritis, while obesity increases the risk fourfold.

Small amounts of weight loss alleviate this stress on our joints. In one study each kilogram of weight loss resulted in a fourfold decrease in the load exerted on the knee in each step taken during daily activities.

Focus on long-term habits

If you’ve ever tried to lose weight but found the kilos return almost as quickly as they left, you’re not alone.

An analysis of 29 long-term weight-loss studies found participants regained more than half of the weight lost within two years. Within five years, they regained more than 80%.

When we lose weight, we take our body out of its comfort zone and trigger its survival response. It then counteracts weight loss, triggering several physiological responses to defend our body weight and “survive” starvation.

Read more: What's the 'weight set point', and why does it make it so hard to keep weight off?

Just as the problem is evolutionary, the solution is evolutionary too. Successfully losing weight long-term comes down to:

• losing weight in small manageable chunks you can sustain, specifically periods of weight loss, followed by periods of weight maintenance, and so on, until you achieve your goal weight

• making gradual changes to your lifestyle to ensure you form habits that last a lifetime.

Setting a goal to reach a healthy weight can feel daunting. But it doesn’t have to be a pre-defined weight according to a “healthy” BMI range. Losing 5–10% of our body weight will result in immediate health benefits.

At the Boden Group, Charles Perkins Centre, we are studying the science of obesity and running clinical trials for weight loss. You can register here to express your interest.