Harvard Research: Drinking Coffee & Weight Loss

Harvard Research: Drinking Coffee & Weight Loss


This is a review of a study published by the Department of Nutrition, at the Harvard T.H. Chan School of Public Health, which looked into coffee consumption and its ability to reduce weight gain.

Coffee and Weight Gain

Coffee is well recognised as having a positive impact on long-term health. Drinking the equivalent of three to four cups of coffee a day reduces the risk of many health conditions including heart disease, type 2 diabetes and some cancers. Most people will gain small amounts of weight each year as they age. But can coffee help prevent this gradual weight gain? Consumption of both caffeinated and decaffeinated coffee has been reported to attenuate long-term weight gain. 

Popular Beverage

Coffee is the most popular beverage in the world, as a drinker you contribute to the more than 400 billion cups that are consumed each, and every year. Indeed, more than 450 million cups of coffee are consumed in the United States every single day, so it’s no secret that coffee brings joy to people all over the world. It can provide a boost in focus, it brings people together socially, and it smells and tastes wonderful.

Is Just Coffee the Best?

A group of researchers have now examined whether drinking an extra cup of coffee a day, or adding sugar, cream or a non-dairy alternative, resulted in more or less weight gain than those who didn't adjust their coffee intake.

Initial Findings

What were the initial findings? People who drank an extra cup of coffee a day gained 0.12 kg (that’s around 0.2 pounds) less weight than expected over that 4-year period. Adding sugar resulted in a fraction more weight gain than expected over the four years, that fraction being 0.09 kg or 32 ounces.

The Studies

The Harvard researchers combined data from 3 large studies from the United States, they were: 

  • Two Nurses' Health Studies from 1986 to 2010, and a study from 1991 to 2015
  • They also looked at a Health Professional Follow-up study from 1991 to 201

The Nurses' Health Studies are two of the largest cohort studies, with more 230,000 participants, which investigates chronic disease risks for women. 

The Health Professional Follow-up study involves more than 50,000 male health professionals and investigates the relationship between diet and health outcomes.

The Analysis

Participants in all three studies completed a baseline questionnaire, and another questionnaire every four years to assess their food and drink intake.

Using the combined datasets, the researchers analyzed changes in coffee intake and changes in the participants' self-reported weight at four-year intervals.

The average four-year weight-gains for the nurses' studies were for the first study 1.2 kg (2.6 pounds) and the second was 1.7 kg (that’s 3.8 pounds), while participants in the health professionals study gained an average of 0.8 kg, that’s around 1.8 pounds. 

The researchers found that increasing un-sweetened caffeinated or decaffeinated coffee intake by one cup a day was associated with a weight gain that was 0.12 kg (around 0.2 pounds) less than expected over the four years.

What about Additives?

Adding creamer (milk) or a non-dairy alternative did not significantly affect this weight change. However, adding sugar (just one teaspoon) to coffee was associated with a weight gain that was 0.09 kg (just under 2 pounds) more than expected over four years. 

These associations were stronger in participants who were younger and had a higher body mass index at the beginning of the studies.

The Unique Study

This study is unique in two ways. It had a very large sample size and followed participants for many years. This adds confidence that the associations were real and can likely be applied to other populations.

Cause for Concern?  

However, there are three reasons to be cautious. First, the findings represent an association, not causation. This means the study does not prove that coffee intake is the true reason for the weight change. Rather, it shows the two changes were observed together over time. 

Second, the findings around weight were very modest. The average four-year weight gain averted, based on one cup of coffee, was 0.12 kilograms, which is about 30 grams per year that’s only 1 ounce. 

The authors say that this amount may not be a meaningful change for most people looking to manage their weight. I’d say that the authors’ use of the phrase “may not be meaningful’ is a massive understatement.

Finally, this analysis did not consider the variability in the amount of caffeine in coffee (which we know can be high), it just assumed a standard amount of caffeine per cup.

Caffeine in Coffee

Caffeine is a natural stimulant which has been shown to temporarily reduce appetite and increase alertness. This may help us to feel less hungry for a short period of time, and this could then potentially lead to reduced energy/calorie intake.

Some people consume coffee before exercising as a stimulant to improve their workout performance, if a workout is more effective, more energy may be expended. However, the benefit is largely thought to be short-lived, rather than long-term.

Caffeine has also been shown to speed up our metabolism, causing more energy to be burned while resting. However, this effect is relatively small and is not a suitable substitute for regular physical activity and a healthy balanced diet.

Another consideration is that coffee has a mild diuretic effect, which can lead to water weight loss. This is water loss, not fat loss, and the weight is quickly regained when you re-hydrate.


If you are pregnant or breastfeeding, it is important to talk to your doctor before increasing your caffeine intake, because caffeine can be passed onto your growing baby. If you need individualized weight guidance, talk to your GP or visit an accredited dietitian.

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