Oil and weight loss: what 14 plant based experts say
Oil is pure fat, about 4,000 calories per pound, the most calorie-dense food there is. Nearly everyone in this guide removes added oil for weight loss; the Pritikin center allows a little.
The differences are in how strict to be, what the reason is (calories, fullness, heart health or brain chemistry) and how much evidence stands behind a total ban.
The statement we compare againstAdded oil should be cut out completely for weight loss.
- Agree 12
- Partly 1
- Disagree 0
- No statement 1
At a glance
| Expert | Position | Evidence behind it |
|---|---|---|
| Walter Kempner | Agrees | Case series, selected for success |
| Nathan Pritikin | Partly agrees | Case series (uncontrolled residential programs) |
| John McDougall | Agrees | Case series (short, residential) |
| Dean Ornish | Agrees | RCT for heart outcomes; modest results in independent weight trials |
| T. Colin Campbell | No clear statement found | – |
| Neal Barnard | Agrees | Randomized controlled trials |
| Hana Kahleova | Agrees | Randomized controlled trials, plus cohort data |
| Alan Goldhamer | Agrees | Narrative review from his own group (2026) |
| Doug Lisle | Agrees | No studies of his own; clinical experience |
| Jeff Novick | Agrees | No studies of his own; summarizes feeding studies |
| Chef AJ | Agrees | Personal story and program reports; no trials |
| Michael Greger | Agrees | Reviews of other people's trials |
| Rip Esselstyn | Agrees | Uncontrolled pilot and event data |
| Peter Rogers | Agrees | No studies of his own; population and mechanism arguments |
What each expert says
-
Walter Kempner
MD
AgreesThe weight-loss diet was rice and fruit with almost no fat, so there was no added oil. That was part of the design rather than a rule he argued for separately.
Evidence: Case series, selected for success
-
Nathan Pritikin
Engineer, no medical degree
Partly agreesThe center allows at most a teaspoon of oil per 1,000 calories and says no oil should be treated as a weight-loss food. Its sample menus still include a little canola oil.
Evidence: Case series (uncontrolled residential programs)
- Pritikin center: the eating planOrganization page
- Pritikin center: 14-day meal plan, day oneOrganization page
-
John McDougall
MD
AgreesNo added oil of any kind, olive and corn oil included, both in his 1994 weight-loss rules and on video.
Evidence: Case series (short, residential)
-
Dean Ornish
MD
AgreesThe program's guidelines exclude added fats and oils and cap fat at 10% of calories, though occasional low-fat packaged foods may contain traces of oil. Ornish himself presents fat as the most calorie-dense part of the diet.
Evidence: RCT for heart outcomes; modest results in independent weight trials
-
T. Colin Campbell
PhD
No clear statement foundNo clear statement found in our sources on this topic. We list nothing rather than guess.
-
Neal Barnard
MD
AgreesPCRM's tested diet had no added fats, and its weight-loss page says trial volunteers kept oils to a minimum.
Evidence: Randomized controlled trials
- PCRM weight-loss pageOrganization page
- Kahleova 2020 trial (Barnard senior author)Study
-
Hana Kahleova
MD, PhD
AgreesHer flagship trial's diet had no added fats at all, with about 10% of calories from fat.
Evidence: Randomized controlled trials, plus cohort data
-
Alan Goldhamer
DC (chiropractor, not a medical doctor)
AgreesGoldhamer's diet has no added salt, oil or sugar, and he tells people who want to lose weight to drop such concentrated foods. A 2026 review from his group is more careful: complete removal is not yet shown to add benefit, though added olive oil may blunt weight loss.
Evidence: Narrative review from his own group (2026)
-
Doug Lisle
PhD
AgreesLisle calls fat slipping past fullness the number one weight problem, citing a study where oil on pasta added about 300 calories with no extra fullness. Apart from weight, he worries about oil mainly when it is heated.
Evidence: No studies of his own; clinical experience
-
Jeff Novick
MS, RDN (registered dietitian)
AgreesNovick points out that two tablespoons of olive oil carry more calories than most premium ice cream, and mocks the idea that it helps weight loss. Oil sits at the top of his density scale.
Evidence: No studies of his own; summarizes feeding studies
-
Chef AJ
Chef and TV host, no medical credential
AgreesOil is one of only three things she says everyone should avoid, with animal products and alcohol. In November 2025, while being treated for cancer, she said she was no longer strictly free of salt, oil and sugar herself.
Evidence: Personal story and program reports; no trials
-
Michael Greger
MD
AgreesGreger lists low added fat among his ingredients for weight loss and notes that one tablespoon of oil adds over 100 calories. He prefers whole-food fats such as nuts to oil.
Evidence: Reviews of other people's trials
-
Rip Esselstyn
Former firefighter and triathlete, no medical credential
AgreesOil goes in week three of his 28-day challenge, and PLANTSTRONG presents itself as fully oil-free. Its blog overstated a 2024 olive-oil trial that did not report weight.
Evidence: Uncontrolled pilot and event data
- Engine 2 keynote (2009) at 27:24
- PLANTSTRONG promise pageOrganization page
- Krenek 2024, J Am Heart AssocStudy
-
Peter Rogers
MD
AgreesRogers bans every oil, olive and omega-3 included: “not one drop.” He also argues that cooking oils damage the brain's hunger center.
Evidence: No studies of his own; population and mechanism arguments
What the evidence says
- No trial has compared an oil-free whole-food plant based diet with the same diet plus oil for weight loss.
- A 2024 crossover trial in 40 adults compared four tablespoons of extra-virgin olive oil a day with under a teaspoon, inside a whole-food plant based diet. Cholesterol and other markers fell on both; weight was not a reported outcome.
- A 2026 review from Goldhamer's own group found no proof yet that removing salt, oil and sugar completely adds benefit beyond a high-quality plant based diet, while suggesting added olive oil may blunt weight loss.
Our reading: The case against oil for weight loss rests on its calorie density, which is not in dispute. A total ban versus a small allowance has not been tested head to head.
Questions
Why do plant based doctors avoid oil for weight loss?
Oil carries about 4,000 calories per pound with no fiber or water, so it adds many calories without filling you up. Several experts in this guide call it the main problem in weight management.
Is olive oil allowed on a plant based weight-loss diet?
Most experts in this guide say no. The Pritikin center allows up to a teaspoon per 1,000 calories.
Has an oil-free diet been tested against one with oil for weight loss?
Not directly. A 2024 trial compared high and low olive oil inside a plant based diet but did not report weight.