Coffee is known to have positive effects on long-term health. Drinking three to four cups of instant coffee a day reduces the risk of many health conditions, including heart disease, type 2 diabetes and some cancers. Most people gain a little weight every year as they age. But can coffee help prevent gradual weight gain?
A group of researchers investigated whether drinking an extra cup of coffee a day or adding sugar, cream or non-dairy alternatives led to more or less weight gain compared to people who didn’t adjust their intake.
Their research (currently a pre-proof, meaning it has been peer-reviewed but has yet to undergo final formatting and copy editing) found a modest association between coffee and less-than-expected weight gain.
Those who drank an extra cup of coffee per day gained 0.12 kilograms less than expected over four years. The addition of sugar increased weight slightly more than expected (0.09 kg) over four years.
How was the study conducted? What was found in it?
The researchers combined data from three large studies in the United States: two Nurses’ Health Studies from 1986 to 2010 and from 1991 to 2015, and a health professional follow-up study from 1991 to 2014.
The Nurses’ Health Studies are the two largest cohort studies, with more than 230,000 participants, and examine chronic disease risks for women. The Health Professional Follow-up study involves more than 50,000 male health professionals and examines the relationship between diet and health outcomes.
Participants in all three studies completed a baseline questionnaire to assess their food and drink intake and another questionnaire every four years. Using the combined dataset, researchers analyzed changes in coffee intake and participants’ self-reported weight over a four-year period.
The average weight gain over four years in the nurses’ study was between 1.2 kg and 1.7 kg, while the participants in the health professionals’ study gained an average of 0.8 kg.
The researchers found that increasing the intake of unsweetened caffeinated or decaffeinated coffee by one cup per day resulted in weight gain that was 0.12 kilograms less than expected over four years.
Adding creamer (milk) or non-dairy alternatives had no significant effect on this weight change.
However, adding sugar (one teaspoon) to coffee led to a weight gain that was 0.09 kg more than expected over four years.
These associations were stronger in participants who were younger and had a higher body mass index at the start of the study.
What are the pros and cons of the study?
This study is unique in two ways. Its sample size was very large and participants were followed for several years. This increases confidence that the association is real and can potentially be extrapolated to other populations.
However, there are three reasons to be cautious.
First, the findings represent an association, not causation. This means that the study does not prove that coffee consumption is the real cause of weight changes. Rather, it shows that the two changes were observed simultaneously over time.
Second, the findings regarding weight were modest. Based on one cup of coffee, an average of 0.12 kilograms of weight gain was prevented over four years, which is about 30 grams per year. This amount may not be a meaningful change for most people looking to control weight.
Finally, this analysis did not take into account variability in the amount of caffeine in coffee (which we know can be high), it just assumed a standard amount of caffeine per cup.
How can coffee help with weight management?
Caffeine is a natural stimulant that has been shown to temporarily reduce appetite and increase alertness. This may help you feel less hungry for a short period of time, potentially reducing energy consumption.
Some people consume coffee before exercise as a stimulant to improve their workout performance – if the workout is more effective, more energy may be expended. However, this benefit is largely believed to be short-term rather than long-term.
Caffeine has also been shown to speed up our metabolism, burning more energy while at rest. However, this effect is relatively small and is not a suitable substitute for regular physical activity and a healthy diet.
Finally, coffee has a mild diuretic effect, which may lead to temporary weight loss due to water. This is water loss, not fat loss, and the weight comes back quickly when you rehydrate.
Is it worth trying coffee for weight loss?
Weight loss can be affected by a variety of factors, so don’t get too excited about the coffee-weight link highlighted in this new study, or increase your coffee intake to unreasonable levels.
Most adults can safely consume about 400 mg of caffeine a day. This is equivalent to two espressos or four cups of instant coffee or eight cups of tea.
If you’re pregnant or breastfeeding, it’s important to talk to your doctor before increasing your caffeine intake, as caffeine can pass to your growing baby.
If you need personalized weight guidance, talk to your GP or see an accredited practicing dietitian.